Lecture V

CHARACTERS OF RETROGRADE VARIETIES

Every one admires the luxuriance of garden-flowers, and their diversity of color and form. All parts of the world have contributed to their number and every taste can find its preference among them. New forms produced by the skill of the breeder are introduced every year. This has been done mostly by crossing and intermingling the characters of introduced species of the same genus. In some of the cases the history of our flowers is so old that their hybrid origin is forgotten, as in the case of the pansies. Hybridizations are still going on in other groups on a large scale, and new forms are openly claimed to be of hybrid origin.

Breeders and amateurs generally have more interest in the results than in the way in which they have been brought about. Excellent flowers and fruit recommend themselves and there seems to be no reason for inquiring about their origin. In some cases the name of the originator may be so widely known that it adds weight to the value of the new form, and therefore may advantageously be coupled with it. The origin and history of the greater part of our garden-flowers, fruits and vegetables are obscure; we see them as they are, and do not know from whence they came. The original habitat for a whole genus or for a species at large, may be known, but questions as to the origin of the single forms, of which it is built up, ordinarily remain unanswered.

For these reasons we are restricted in most cases to the comparison of the forms before us. This comparison has led to the general use of the term "variety" in opposition to "species." The larger groups of forms, which are known to have been introduced as such are called species. All forms which by their characters belong to such a species are designated as varieties, irrespective of their systematic relation to the form, considered as the ancestor of the group.

Hence, we distinguish between "hybrid varieties" and "pure varieties" according to their origin from different parents or from a single line of ancestors. Moreover, in both groups the forms may be propagated by seeds, or in the vegetative way by buds, by grafting or by cutting, and this leads to the distinction of "seed-varieties" and "vegetative varieties." In the first case the inheritance of the special characters through the seeds decides the status of the variety, in the latter case this point is left wholly out of consideration.

Leaving aside all these different types, we are concerned here only with the "seed-varieties" of pure origin, or at least with those, that are supposed to be so. Hybridization and vegetative multiplication of the hybrids no doubt occur in nature, but they are very rare, when compared with the ordinary method of propagation by seed. "Seed-varieties" may further be divided into constant and inconstant ones. The difference is very essential, but the test is not always easy to apply. Constant varieties are as sharply defined and as narrowly limited as are the best wild species, while inconstant types are cultivated chiefly on account of their wide range of form and color. This diversity is repeated yearly, even from the purest seed. We will now discuss the constant seed-varieties, leaving the inconstant and eversporting types to a subsequent lecture.

In this way we may make an exact inquiry into the departures from the species which are ordinarily considered to constitute the essential character of such a constant and pure seed-variety and need only compare these differences with those that distinguish the elementary species of one and the same group from each other.

Two points are very striking. By far the greatest part of the ordinary garden-varieties differ from their species by a single sharp character only. In derivative cases two, three or even more such characters may be combined in one variety, for instance, a dwarfed variety of the larkspur may at the same time bear white flowers, or even double white flowers, but the individuality of the single characters is not in the least obscured by such combinations.

The second point is the almost general occurrence of the same variety in extended series of species. White and double flowers, variegated leaves, dwarfs and many other instances may be cited. It is precisely this universal repetition of the same character that strikes us as the essential feature of a variety.

And again these two characteristics may now be considered separately. Let us begin with the sharpness of the varietal characters. In this respect varieties differ most obviously from elementary species. These are distinguished from their nearest allies in almost all organs. There is no prominent distinctive feature between the single forms of Draba Verna, Helianthemum or of Taraxacum; all characters are almost equally concerned. The elementary species of Draba are characterized, as we have seen, by the forms and the hairiness of the leaves, the number and height of the flower-stalks, the breadth and incision of the petals, the forms of the fruits, and so on. Every one of the two hundred forms included in this collective species has its own type, which it is impossible to express by a single term. Their names are chosen arbitrarily. Quite the contrary is the case with most of the varieties, for which one word ordinarily suffices to express the whole difference.

White varieties of species with red or blue flowers are the most common instances. If the species has a compound color and if only one of the constituents is lost, partially colored types arise as in Agrostemma Coronaria bicolor. Or the spots may disappear and the color become uniform as in Gentiana punctata concolor and the spotless Arum or Arum maculatum immaculatum. Absence of hairs produces forms as Biscutella laevigata glabra; lack of prickles gives the varieties known as inermis, as for instance, Ranunculus arvensis inermis. Cytisus prostratus has a variety ciliata, and Solanum Dulcamara, or the bitter-sweet, has a variety called tomentosum_. The curious monophyllous variety of the strawberry and many other forms will be discussed later.

To enlarge this list it would only be necessary to extract from a flora, or from a catalogue of horticultural plants, the names of the varieties enumerated therein. In nearly every instance, where true varieties and not elementary species are concerned, a single term expresses the whole character.

Such a list would also serve to illustrate the second point since the same names would recur frequently. Long lists of varieties are called alba, or inermis, or canescens or lutea, and many genera contain the same appellations. In some instances the systematists use a diversity of names to convey exactly the same idea, as if to conceal the monotony of the character, as for instance in the case of the lack of hairs, which is expressed by the varietal names of Papaver dubium glabrum, Arabis ciliata glabrata, Arabis hirsuta glaberrima, Veronica spicata nitens, Amygdalus persica laevis, Paeonia corallina Leiocarpa, &c.

On the contrary we find elementary species in different genera based on the greatest possible diversity of features. The forms of Taraxacum or Helianthemum do not repeat those of Draba or Viola. In roses and brambles the distinguishing features are characteristic of the type, as they are evidently derived from it and limited to it. And this is so true that nobody claims the grade of elementary species for white roses or white brambles, but everyone recognizes that forms diverging from the nearest species by a single character only, are to be regarded as varieties.

This general conviction is the basis on which we may build up a more sharply defined distinction between elementary species and varieties. It is an old rule in systematic botany, that no form is to be constituted a species upon the basis of a single character. All authors agree on this point; specific differences are derived from the totality of the attributes, not from one organ or one quality. This rule is intimately connected with the idea that varieties are derived from species. The species is the typical, really existing form from which the variety has originated by a definite change. In enumerating the different forms the species is distinguished by the term of genuine or typical, often only indicated as a or the first; then follow the varieties sometimes in order of their degree of difference, sometimes simply in alphabetical order. In the case of elementary species there is no real type; no one of them predominates because all are considered to be equal in rank, and the systematic species to which they are referred is not a really existing form, but is the abstraction of the common type of all, just as it is in the case of a genus or of a family.

Summarizing the main points of this discussion, we find that elementary species are of equal rank and together build up the collective or systematic ideal species. Varieties on the other hand are derived from a real and commonly, still existing type.

I hope that I have succeeded in showing that the difference between elementary species, or, as they are often called, smaller or subspecies, on the one hand and varieties on the other, is quite a marked one. However, in order to recognize this principle it is necessary to limit the term variety, to those propagating themselves by seed and are of pure and not of hybrid origin.

But the principle as stated here, does not involve an absolute contrast between two groups of characters. It is more a difference in our knowledge and appreciation of them than a difference in the things themselves. The characters of elementary species are, as a rule, new to us, while those of varieties are old and familiar. It seems to me that this is the essential point.

And what is it that makes us familiar with them? Obviously the continuous recurrence of the same changes, because by a constant repetition they must of course lose their novelty.

Presently we shall look into these characters more in detail and then we shall find that they are not so simple as might be supposed at first sight; but precisely because we are so familiar with them, we readily see that their different features really belong to a single character; while in elementary species everything is so new that it is impossible for us to discern the unities of the new attributes.

If we bear in mind all these difficulties we cannot wonder at the confusion on this question that seems to prevail everywhere. Some authors following Linnaeus simply call all the subdivisions of species, varieties; others follow Jordan and avoid the difficulty by designating all smaller forms directly as species. The ablest systematists prefer to consider the ordinary species as collective groups, calling their constituents "The elements of the species," as was done by A.P. De Candolle, Alph. De Candolle and Lindley.

By this method they clearly point out the difference between the subdivisions of wild species as they ordinarily occur, and the varieties in our gardens, which would be very rare, were they not singled out and preserved.

Our familiarity with a character and our grounds for calling it an old acquaintance may result from two causes, which in judging a new variety are essentially different. The character in question may be present in the given species or it may be lacking, but present in the other group. In the first case a variety can only be formed by the loss of the character, in the second case it arises by the addition of a new one.

The first mode may be called a negative process, while the second is then to be designated as positive. And as it is more easy to lose what one has than to obtain something new, negative varieties are much more common than are positive ones.

Let us now take an instance of a character that is apt to vary in both ways, for this is obviously the best way of making clear what is meant by a negative and a positive change.

In the family of the composites we find a group of genera with two forms of florets on each flower-head. The hermaphrodite ones are tubular with 5, or rarely 4, equal teeth, and occupy the center of the head. These are often called the flosculous florets or disk-florets. Those of the circumference are ligulate and ordinarily unisexual, without stamens. In many cases they are sterile, having only an imperfect ovary. They are large and brightly colored and are generally designated as ray-florets. As instances we may cite the camomile (Anthemis nobilis), the wild camomile (Matricaria Chamomilla), the yarrow (Achillea Millefolium), the daisies, the Dahlia and many others. Species occur in this group of plants from time to time that lack the ray-florets, as in the tansy (Tanacetum vulgare) and some artemisias. And the genus of the marigolds or Bidens is noted for containing both of these types. The smaller and the three-toothed marigold (B. cernua and B. tripartita) are very common plants of wet soil and swamps, ordinarily lacking the ray-florets, and in some countries they are very abundant and wholly constant in this respect, never forming radiate flower-heads. On the other hand the white-flowered and the purple marigold (B. leucantha and B. atropurpurea) are cultivated species of our gardens, prized for their showy flower-heads with large white or deeply colored, nearly black-purple florets.

Here we have opportunity to observe positive and negative varieties of the same character. The smaller, and the three-toothed marigold occur from time to time, provided with ray florets, showing a positive variation. And the white marigold has produced in our gardens a variety without rays. Such varieties are quite constant, never returning to the old species. Positive and negative varieties of this kind are by no means rare among the compositae.

In systematic works the positive ones are as a rule called "radiate," and the negative ones "discoid." Discoid forms of the ordinary camomile, of the daisy, of some asters (Aster Tripolium), and of some centauries have been described. Radiate forms have been observed in the tansy (Tanacetum vulgare), the common horse-weed or Canada fleabane (Erigeron canadensis) and the common groundsel (Senecio vulgaris). Taken broadly the negative varieties seem to be somewhat more numerous than the positive ones, but it is very difficult to come to a definite conclusion on this point.

Quite the contrary is the case with regard to the color-varieties of red and blue flowers. Here the loss of color is so common that every one could give long lists of examples of it. Linnaeus himself supposed that no blue or red-colored wild species would be without a white variety. It is well known that he founded his often criticized prescript never to trust to color in recognizing or describing a species, on this belief.

On the other hand there are some red varieties of white-flowered species. But they are very rare, and little is known about their characters or constancy. Blue varieties of white species are not found. The yarrow (Achillea Millefolium) has a red-flowered form, which occurs from time to time in sunny and sandy localities. I have isolated it and cultivated it during a series of years and during many generations. It is quite true to its character, but the degree of its coloring fluctuates between pink and white and is extremely variable. Perhaps it can be considered as an inconstant variety. A redflowered form of the common Begonia semperflorens is cultivated under the name of "Vernon," the white hawthorn (Crataegus Oxyacantha) is often seen with red flowers, and a pink-flowered variety of the "Silverchain" or "Bastard acacia" (Robinia Pseud-Acacia) is not rarely cultivated. The "Crown" variety of the yellow wall-flower and the black varieties, are also to be considered as positive color variations, the black being due in the latter cases to a very great amount of the red pigment.

Among fruits there are also some positive red varieties of greenish or yellowish species, as for instance the red gooseberry (Ribes Grossularia) and the red oranges. The red hue is far more common in leaves, as seen among herbs, in cultivated varieties of Coleus and in the brown leaved form of the ordinary white clover, among trees and shrubs in the hazelnut (Corylus), the beech (Fagus), the birch (Betula), the barberry (Berberis) and many others. But though most of these forms are very ornamental and abundant in parks and gardens, little is as yet known concerning the origin of their varietal attributes and their constancy, when propagated by seeds. Besides the ray-florets and the colors, there are of course a great many other characters in which varieties may differ from their species. In most of the cases it is easy to discern whether the new character is a positive or a negative one. And it is not at all necessary to scrutinize very narrowly the list of forms to become convinced that the negative form is the one which prevails nearly everywhere, and that positive aberrations are in a general sense so rare that they might even be taken for exceptions to the rule.

Many organs and many qualities may be lost in the origination of a variety. In some instances the petals may disappear, as in Nigella, or the stamens, as in the Guelder-rose (Viburnum Opulus) and the Hortensia and in some bulbs even the whole flowers may be wanting, as in the beautiful "Plumosa" form of the cultivated grape-hyacinth or Muscari comosum. Fruits of the pineapples and bananas without seeds are on record as well as some varieties of apples and pears, of raisins and oranges. And some years ago Mr. Riviere of Algeria described a date growing in his garden that forms fruit without pits. The stoneless plum of Mr. Burbank of Santa Rosa, California, is also a very curious variety, the kernel of which is fully developed but naked, no hard substance intervening between it and the pulp.

More curious still are the unbranched varieties consisting of a single stem, as may be seen sometimes in the corn or maize and in the fir. Fir-trees of some three or four meters in height without a single branch, wholly naked and bearing leaves only on the shoots of the last year's growth at the apex of the tree, may be seen. Of course they cannot bear seed, and so it is with the sterile maize, which never produces any seed-spikes or staminate flowers. Other seedless varieties can be propagated by buds; their origin is in most cases unknown, and we are not sure as to whether they should be classified with the constant or with the inconstant varieties.

A very curious loss is that of starch in the grains of the sugar-corn and the sugar-peas. It is replaced by sugar or some allied substance (dextrine). Equally remarkable is the loss of the runners in the so-called "Gaillon" strawberries.

Among trees the pendulous or weeping, and the broomlike or fastigiate forms are very marked varieties, which occur in species belonging to quite different orders. The ash, the beach, some willows, many other trees and some finer species of garden-plants, as Sophora japonica, have given rise to weeping varieties, and the yew-tree or Taxus has a fastigiate form which is much valued because of its ascending branches and pyramidal habit. So it is with the pyramidal varieties of oaks, elms, the bastard-acacia and some others.

It is generally acknowledged that these forms are to be considered as varieties on the ground of their occurrence in so wide a range of species, and because they always bear the same attributes. The pendulous forms owe their peculiarity to a lengthening of the branches and a loss of their habit of growing upwards; they are too weak to retain a vertical position and the response to gravity, which is ordinarily the cause of the upright growth, is lacking in them. As far as we know, the cause of this weeping habit is the same in all instances. The fastigiate trees and shrubs are a counterpart of the weeping forms. Here the tendency to grow in a horizontal direction is lacking, and with it the bilateral and symmetric structure of the branches has disappeared. In the ordinary yew-tree the upright stem bears its needles equally distributed around its circumference, but on the branches the needles are inserted in two rows, one to the left and one to the right. All the needles turn their upper surfaces upwards, and their lower surfaces downwards, and all of them are by this means placed in a single horizontal plane, and branching takes place in the same plane. Evidently this general arrangement is another response to gravity, and it is the failure of this reaction which induces the branches to grow upwards and to behave like stems.

Both weeping and fastigiate characters are therefore to be regarded as steps in a negative direction, and it is highly important that even such marked departures occur without transitions or intermediate forms. If these should occur, though ever so rarely, they would probably have been brought to notice, on account of the great prospect the numerous instances would offer. The fact that they are lacking, proves that the steps, though apparently great, are in reality to be considered as covering single units, that cannot be divided into smaller parts. Unfortunately we are still in the dark as to the question of the inheritance of these forms, since in most cases it is difficult to obtain pure seed.

We now consider the cases of the loss of superficial organs, of which the nectarines are example. These are smooth peaches, lacking the soft hairy down, that is a marked peculiarity of the true peaches. They occur in different races of the peach. As early as the beginning of the past century, Gallesio described no less than eight subvarieties of nectarines, each related to a definite race of peach. Most of them reproduce themselves truly from seed, as is well known in this country concerning the clingstones, freestones and some other types. Nectarines have often varied, giving rise to new sorts, as in the case of the white nectarine and many others differing greatly in appearance and flavor. On the other hand it is to be remarked, that the trees do not differ in other respects and cannot be distinguished while young, the varietal mark being limited to the loss of the down on the fruit. Peaches have been known to produce nectarines, and nectarines to yield true peaches. Here we have another instance of positive and negative steps with reference to the same character, but I cannot withhold an expression of some doubt as to the possibility of crossing and subsequently splitting up of the hybrids as a more probable explanation of at least some of the cases quoted by various writers.

Smooth or glabrous varieties often occur, and some of them have already been cited as instances of the multiplication of varietal names. Positive aberrations are rather rare, and are mostly restricted to a greater density of the pubescence in some hairy species, as in Galeopsis Ladanum canescens, Lotus corniculatus hirsutus and so on. But Veronica scutellata is smooth and has a pubescent variety, and Cytisus prostratus and C. spinescens are each recorded to have a ciliate form.

Comparable with the occurrence and the lack of hairs, is the existence or deficiency of the glaucous effect in leaves, as is well known in the common Ricinus. Here the glaucous appearance is due to wax distributed in fine particles over the surface of the leaves, and in the green variety this wax is lacking. Other instances could be given as in the green varieties of Papaver alpinum and Rumex scutatus. No positive instances are recorded in this case.

Spines and prickles may often disappear and give rise to unarmed and defenceless types. Of the thorn-apples both species, the whiteflowered Datura Stramonium and the purple D. Tatula have such varieties. Spinach has a variety called the "Dutch," which lacks the prickles of the fruit; it is a very old form and absolutely constant, as are also the thornless thorn-apples. Last year a very curious instance of a partial loss of prickles was discovered by Mr. Cockerell of East Las Vegas in New Mexico. It is a variety of the American cocklebur, often called sea-burdock, or the hedgehog-burweed, a stout and common weed of the western states. Its Latin name is Xanthium canadense or X. commune and the form referred to is named by Mr. Cockerell, X. Wootoni, in honor of Professor E.o. Wooton who described the first collected specimens.

The burs of the common species are densely covered with long prickles, which are slightly hooked at the apex. In the new form, which is similar in all other respects to the common cocklebur, the burs are more slender and the prickles much less numerous, about 25 to the bur and mostly stouter at the base. It occurs abundantly in New Mexico, always growing with the common species, and seems to be quite constant from seed. Mr. Cockerell kindly sent me some burs of both forms, and from these I raised in my garden last year a nice lot of the common, as well as of the Wootoni plants.

Spineless varieties are recorded for the bastard-acacia, the holly and the garden gooseberry (Ribes Grossularia, or R. Uva-crispa). A spineless sport of the prickly Broom (Ulex europaeus) has been seen from time to time, but it has not been propagated.

Summarizing the foregoing facts, we have excellent evidence of varieties being produced either by the loss of some marked peculiarity or by the acquisition of others that are already present in allied species. There are a great many cases however, in which the morphologic cause of the dissimilarity is not so easily discerned. But there is no reason to doubt that most of them will be found to conform to the rule on closer investigation. Therefore we can consider the following as the principal difference between elementary species and varieties; that the first arise by the acquisition of entirely new characters, and the latter by the loss of existing qualities or by the gain of such peculiarities as may already be seen in other allied species.

If we suppose elementary species and varieties originated by sudden leaps or mutations, then the elementary species have mutated in the line of progression, some varieties have mutated in the line of retrogression, while others have diverged from their parental types in a line of depression, or in the way of repetition. This conception agrees quite well with the current idea that in the building up of the vegetable kingdom according to the theory of descent, it is species that form the links of the chain from the lower forms to the more highly organized later derivatives. Otherwise expressed, the system is built up of species, and varieties are only local and lateral, but never of real importance for the whole structure.

Heretofore we have generally assumed, that varieties differ from the parent-species in a single character only, or at least that only one need be considered. We now come to the study of those varieties, which differ in more than one character. Of these there are two types. In the first the points of dissimilarity are intimately connected with one another, in the second they are more or less independent.

The mutually related peculiarities may be termed correlative, and we therefore speak, in such cases, of correlative variability. This phenomenon is of the highest importance and is of general occurrence. But before describing some examples, it is as well to note that in the lecture on fluctuating variability, cases of a totally different nature will be dealt with, which unfortunately are designated by the same term. Such merely fluctuating variations are therefore to be left out of the present discussion.

The purple thorn-apple, which is considered by some writers as a variety of the white-flowered species or Datura Stramonium, and by others as a separate species, D. Tatula, will serve as an illustration. But as its distinguishing attributes, as far as we are concerned with them here, are of the nature described above as characteristic of varietal peculiarities no objection can be made to our using them as a case of correlative variability.

The essential character of the purple thornapple lies in the color of the flowers, which are of a very beautiful pale blue. But this color is not limited to the corolla. It is also to be seen in the stems and in the stalks and veins of the leaves, which are stained with a deep purple, the blue color being added to the original green. Even on the surface of the leaves it may spread into a purplish hue. On the stems it is to be met with everywhere, and even the young seedlings show it. This is of some importance, as the young plants when unfolding their cotyledons and primary leaves, may be distinguished by this means from the seedlings of the white flowered species.

In crossing experiments it is therefore possible to distinguish the whites and the blues, even in young seedlings, and experience shows that the correlation is quite constant. The color can always be relied upon; if lacking in the seedlings, it will be lacking in the stems and flowers also; but if the axis of the young plant is ever so slightly tinged, the color will show itself in its beauty in the later stages of the life of the plant.

This is what we term correlation. The colors of the different organs are always in agreement. It is true that they require the concurrence of light for development, and that in the dark or in a faint light the seedlings are apt to remain green when they should become purple, but aside from such consideration all organs always come true to their color, whether pure green and white, or whether these are combined with the blue tinge. This constancy is so absolute that the colors of the different organs convey the suggestion, that they are only separate marks of a single character.

It is on this suggestion that we must work, as it indicates the cause of the correlation. Once present, the faculty of producing the anthocyan, the color in question, will come into activity wherever and whenever opportunity presents itself. It is the cell-sap of the ordinary cell tissue or parenchyma, which is colored by the anthocyan, and for this reason all organs possessing this tissue, may exhibit the color in question.

Thus the color is not a character belonging to any single organ or cell, nor is it bound to a morphologic unit; it is a free, physiologic quality. It is not localized, but belongs to the entire plant. If we wish to assume for its basis material representative particles, these particles must be supposed to be diffused throughout the whole body of the plant.

This conception of a physiologic unit as the cause of colors and other qualities is evidently opposed to the current idea of the cells and tissues as the morphologic units of the plants. But I do not doubt, that in the long run it will recommend itself as much to the scientist as to the breeder. For the breeder, when desiring to keep his varieties up to their standard, or when breeding to a definite idea, obviously keeps his standard and his ideal for the whole plant, even if he breeds only for flowers or for fruit.

I have chosen the color of the purple thornapple as a first example, but the colors of other plants show so many diverging aspects, all pointing so clearly to the same conclusion, that it would be well to take a more extensive view of this interesting subject.

First we must consider the correlation in the colors of flowers and fruits. If both are colored in the species, whether red or brown or purple or nearly black, and a variety lacking this hue is known, it will be lacking in both organs. If the color is pure, the flowers and berries will become white, but such cases are rare. Ordinarily a yellowish or greenish tinge underlies the ornamental color, and if this latter disappears, the yellowish ground will become manifest. So for instance in the Belladonna, a beautiful perennial herb with great shiny black, but very poisonous, fruits. Its flowers are brown, but in some woods a variety with greenish flowers and bright yellow berries occurs, which is also frequently seen in botanic gardens. The anthocyan dye is lacking in both organs, and the same is the case with the stems and the leaves. The lady's laurel or Daphne Mezereum has red corollas, purple leaves and red fruits; its white flowered variety may be distinguished by lack of the red hue in the stems and leaves, and by their beautiful yellow berries. Many other instances could be given, since the loss of color in berries is a very common occurrence, so common that for instance, in the heath-family or Ericaceae, with only a few exceptions, all berry-bearing species have white-fruited varieties.

The same correlation is observed in the seeds. The white-flowered flax may be seen to yield yellow and not brown seeds as in the blue species. Many varieties of flowers may be recognized by the color of their seeds, as in the poppies, stocks and others. Other white-flowered varieties may be distinguished when germinating, their young axes being of a pure instead of a purplish green. It is a test ordinarily used by gardeners, to purify their flower beds long before the blooming time, when thinning or weeding them. Even in wild plants, as in Erodium, Calluna, Brunella and others, a botanist may recognize the rare white-flowered variety by the pure green color of the leaves, at times when it is not in flower. Some sorts of peas bear colored flowers and a red mark on the stipules of their leaves. Among bulbous plants many varieties may be recognized even in the dry bulbs by the different tinges of the outer scales.

Leaving the colors, we come now to another instance of correlation, which is still more astonishing. For it is as rare, as color-varieties are common. It is afforded by some plants the leaves of which, instead of being entire or only divided into large parts, are cleft to a greater extent by repeated fissures of the marginal lobes. Such foliar variations are often seen in gardens, where they are cultivated for their beauty or singularity, as the laciniated alders, fern-leaved, beeches and limes, oakleaved laburnums, etc. Many of them are described under the varietal name of laciniata. In some cases this fissure extends to the petals of the flowers, and changes them in a way quite analogous to the aberrancy of the leaves.

This is known to occur with a variety of brambles, and is often seen in botanic gardens in one of the oldest and most interesting of all anomalies, the laciniated variety of the greater celandine or Chelidonium majus. Many other instances could be given. Most of them belong to the group of negative variations, as we have defined them. But the same thing occurs also with positive varieties, though of course, such cases are very rare. The best known instance is that of the ever-flowering begonia, Begonia semperflorens, which has green leaves and white flowers, but which has produced garden varieties with a brown foliage and pink flowers. Here also the new quality manifests itself in different organs.

Enough has now been said on correlative changes, to convince us that they are as a rule to be considered as the expression of some general internal or physiologic quality, which is not limited to a single organ, but affects all parts of the organism, provided they are capable of undergoing the change. Such characters are therefore to be considered as units, and should be referred to the group of single characters.

Opposed to these are the true compound characters, which consist of different units. These may be segregated by the production of varieties, and thereby betray the separate factors of the complex group.

The most beautiful instances of such complex characters are offered by the colors of some of the most prized garden-flowers. Rarely these are of a single hue, often two or three shades contribute to the effect, and in some cases special spots or lines or tracings are to be seen on a white or on a colored background. That such spots and lines are separate units is obvious and is demonstrated by the fact that sometimes spotless varieties occur, which in all other respects have kept the colors of the species. The complexity of the color is equally evident, whenever it is built up of constituents of the anthocyan and of the yellow group. The anthocyan dye is limited to the sap-cavity of the cells, while the yellow and pure orange colors are fixed in special organs of the protoplasm. The observation under the microscope shows at once the different units, which though lying in the same cell and in almost immediate vicinity of each other are always wholly separated from one another by the wall of the vacuole or sapfilled cell-cavity.

The combination of red and yellow gives a brown tinge, as in the cultivated wall-flower, or those bright hues of a dark orange-red, which are so much sought in tulips. By putting such flowers for a short time in boiling water, the cells die and release the red pigment, which becomes diffused in the surrounding fluids and the petals are left behind with their yellow tinge. In this way it is easy to separate the constituents, and demonstrate the compound nature of the original colors.

But the diversity of the color patterns is far from being exhausted with these simple instances. Apart from them, or joined to them, other complications are frequently seen, which it is impossible to analyze in such an artificial way. Here we have to return to our former principle, the comparison of different varieties. Assuming that single units may be lost, irrespective of the others, we may expect to find them segregated by variation, wherever a sufficiently wide range of color-varieties is in cultivation. In fact, in most cases a high degree of dissimilarity may be reached in the simplest way by such a separation of the components, and by their combination into most diverse smaller groups. A very nice instance of such an analysis of flower-colors is afforded by the ordinary snapdragon. The beautiful brown red color of this common garden-plant is composed on one side of yellow elements, on the other of red units. Of the yellow there are two, one staining the whole corolla with a light hue, as is to be seen in the pure yellow variety called _luteum. This form has been produced by the loss of the whole group of the red constituents. If the yellow tinge is also lost, there arises a white variety, but this is not absolutely colorless, but shows the other yellow constituent. This last stains only some small parts of the lips of the flower around the throat, brightening, as it seems, the entrance for the visiting insects. In many of the red or reddish varieties this one yellow patch remains, while the general yellow hue fails. In the variety called "Brilliant" the yellow ground makes the red color more shiny, and if it is absent the pure carmine tinge predominates.

It is readily seen, that in the ordinary form the lips are of a darker red than the tube. This evident dissimilarity indicates some complexity. And in fact we have two varieties which exhibit the two causes of this attribute separately. One of them is called "Delila," and has the red color limited to the lips, whilst the tube is pure white. The other is called "Fleshy," and is of a pale pink throughout the whole corolla. Adding these two units to one another, we get the original dark red of the wild type, and it may be briefly stated here, that the way of effecting such an addition is given us in the crossing of the "Fleshy" and the "Delila" variety, the hybrid showing the two colors and returning thereby to the old prototype.

Other cases of compound flower colors or of color patterns might be given as in the Mimulus and the poppy, and in most of these cases some varieties are to be seen in our gardens which show only the single constituents of the group.

Many dark flowers have an intermediate bright hued form besides the white variety, as in the case of roses, asters, Nicandra and so on.

Intermediate forms with respect to stature may also be seen. The opium-poppy, the snapdragon, peas, the Nicandra, and many other garden-plants have not only dwarf varieties, but also some of intermediate height. These, though they are intermediate between the tall and dwarf types, cannot be considered as transitions, as between them and the extremes, intermediates are, as a rule wholly lacking. Instances of the same occurrence of three types may be seen in the seeds of maize ("Cuzco," "Horse-dent" and "Gracillima") of beans and some other plants. The Xanthium Wootoni, above referred to, with only part of the prickles of Xanthium commune is also a very curious instance of the demonstration of the compound nature of a character.

Summarizing the conclusions that may be drawn from the evidence given in this lecture, we have seen that varieties differ from elementary species in that they do not possess anything really new. They originate for the greater part in a negative way, by the apparent loss of some quality, and rarely in a positive manner by acquiring a character, already seen in allied species. These characters are not of the nature of morphologic entities, but are to be considered as physiologic units, present in all parts of the organisms, and manifesting themselves where ever occasion is afforded. They are units in the sense that they may appear and disappear singly. But very often they are combined to yield compound characters, which are capable of analysis. Opportunities for such an analysis are afforded by these groups of cultivated varieties, of which some members show a single distinguishing quality, or a number of them.