Lecture Ii

ELEMENTARY SPECIES IN NATURE

What are species? Species are considered as the true units of nature by the vast majority of biologists. They have gained this high rank in our estimation principally through the influence of Linnaeus. They have supplanted the genera which were the accepted units before Linnaeus. They are now to be replaced in their turn, by smaller types, for reasons which do not rest upon comparative studies but upon direct experimental evidence.

Biological studies and practical interests alike make new demands upon systematic botany. Species are not only the subject-material of herbaria and collections, but they are living entities, and their life-history and life-conditions command a gradually increasing interest. One phase of the question is to determine the easiest manner to deal with the collected forms of a country, and another feature is the problem as to what groups are real units and will remain constant and unchanged through all the years of our observations.

Before Linnaeus, the genera were the real units of the system. De Candolle pointed out that the old common names of plants, such as roses and clover, poplars and oaks, nearly all refer to genera. The type of the clovers is rich in color, and the shape of the flower-heads and the single flowers escape ordinary observation; but notwithstanding this, clovers are easily recognized, even if new types come to hand. White and red clovers and many other species are distinguished simply by adjectives, the generic name remaining the same for all.

Tournefort, who lived in the second half of the 17th century (1656-1708), is generally considered as the author of genera in systematic botany. He adopted, what was at that time the general conception and applied it throughout the vegetable kingdom. He grouped the new and the rare and the previously overlooked forms in the same manner in which the more conspicuous plants were already arranged by universal consent. Species were distinguished by minor marks and often indicated by short descriptions, but they were considered of secondary importance.

Based on the idea of a direct creation of all living beings, the genera were then accepted as the created forms. They were therefore regarded as the real existing types, and it was generally surmised that species and varieties owed their origin to subsequent changes under the influence of external conditions. Even Linnaeus agreed with this view in his first treatises and in his "Philosophical Botany" he still kept to the idea that all genera had been created at once with the beginning of life.

Afterwards Linnaeus changed his opinion on this important point, and adopted species as the units of the system. He declared them to be the created forms, and by this decree, at once reduced the genera to the rank of artificial groups. Linnaeus was well aware that this conception was wholly arbitrary, and that even the species are not real indivisible entities. But he simply forbade the study of lesser subdivisions. At his time he was quite justified in doing so, because the first task of the systematic botanists was the clearing up of the chaos of forms and the bringing of them into connection with their real allies.

Linnaeus himself designated the subdivisions of the species as varieties, but in doing so he followed two clearly distinct principles. In some cases his species were real plants, and the varieties seemed to be derived from them by some simple changes. They were subordinated to the parent-species. In other cases his species were groups of lesser forms of equal value, and it was not possible to discern which was the primary and which were the derivatives.

These two methods of subdivision seem in the main, and notwithstanding their relatively imperfect application in many single examples, to correspond with two really distinct cases. The derivative varieties are distinguished from the parent-species by some single, but striking mark, and often this attribute manifests itself as the loss of some apparent quality. The loss of spines and of hairs and the loss of blue and red flower-colors are the most notorious, but in rarer cases many single peculiarities may disappear, thereby constituting a variety. This relation of varieties to the parent-species is gradually increasing in importance in the estimation of botanists, sharply contrasting with those cases, in which such dependency is not to be met with.

If among the subdivisions of a species, no single one can be pointed out as playing a primary part, and the others can not be traced back to it, the relation between these lesser units is of course of another character. They are to be considered of equal importance. They are distinguished from each other by more than one character, often by slight differences in nearly all their organs and qualities. Such forms have come to be designated as "elementary species." They are only varieties in a broad and vague systematic significance of the word, not in the sense accorded to this term in horticultural usage, nor in a sharper and more scientific conception.

Genera and species are, at the present time, for a large part artificial, or stated more correctly, conventional groups. Every systematist is free to delimit them in a wider or in a narrower sense, according to his judgment. The greater authorities have as a rule preferred larger genera, others of late have elevated innumerable subgenera to the rank of genera. This would work no real harm, if unfortunately, the names of the plants had not to be changed each time, according to current ideas concerning genera. Quite the same inconstancy is observed with species. In the Handbook of the British Flora, Bentham and Hooker describe the forms of brambles under 5 species, while Babington in his Manual of British Botany makes 45 species out of the same material. So also in other cases. For instance, the willows which have 13 species in one and 31 species in the other of these manuals, and the hawkweeds for which the figures are 7 and 32 respectively. Other authors have made still greater numbers of species in the same groups.

It is very difficult to estimate systematic differences on the ground of comparative studies alone. All sorts of variability occur, and no individual or small group of specimens can really be considered as a reliable representative of the supposed type. Many original diagnoses of new species have been founded on divergent specimens and of course, the type can afterwards neither be derived from this individual, nor from the diagnosis given.

This chaotic state of things has brought some botanists to the conviction that even in systematic studies only direct experimental evidence can be relied upon. This conception has induced them to test the constancy of species and varieties, and to admit as real units only such groups of individuals as prove to be uniform and constant throughout succeeding generations. The late Alexis Jordan, of Lyons in France, made extensive cultures in this direction. In doing so, he discovered that systematic species, as a rule, comprise some lesser forms, which often cannot easily be distinguished when grown in different regions, or by comparing dried material. This fact was, of course, most distasteful to the systematists of his time and even for a long period afterwards they attempted to discredit it. Milde and many others have opposed these new ideas with some temporary success. Only of late has the school of Jordan received due recognition, after Thuret, de Bary, Rosen and others tested its practices and openly pronounced for them. Of late Wittrock of Sweden has joined them, making extensive experimental studies concerning the real units of some of the larger species of his country.

From the evidence given by these eminent authorities, we may conclude that systematic species, as they are accepted nowadays, are as a rule compound groups. Sometimes they consist of two or three, or a few elementary types, but in other cases they comprise twenty, or fifty, or even hundreds of constant and well differentiated forms.

The inner constitution of these groups is however, not at all the same in all cases. This will be seen by the description of some of the more interesting of them. The European heartsease, from which our garden-pansies have been chiefly derived, will serve as an example. The garden-pansies are a hybrid race, won by crossing the Viola tricolor with the large flowered and bright yellow V. lutea. They combine, as everyone knows, in their wide range of varieties, the attributes of the latter with the peculiarities of the former species.

Besides the lutea, there are some other species, nearly allied to tricolor, as for instance, cornuta, calcarata, and altaica, which are combined with it under the head of Melanium as a subgenus, and which together constitute a systematic unity of undoubted value, but ranging between the common conceptions of genus and species. These forms are so nearly allied to the heartsease that they have of late been made use of in crosses, in order to widen the range of variability of garden-pansies.

Viola tricolor is a common European weed. It is widely dispersed and very abundant, growing in many localities in large numbers. It is an annual and ripens its seeds freely, and if opportunity is afforded, it multiplies rapidly.

Viola tricolor has three subspecies, which have been elevated to the rank of species by some authors, and which may here be called, for brevity's sake, by their binary names. One is the typical V. tricolor, with broad flowers, variously colored and veined with yellow, purple and white. It occurs in waste places on sandy soil. The second is called V. arvensis or the field-pansy; it has small inconspicuous flowers, with pale-yellowish petals which are shorter than the sepals. It pollinates itself without the aid of insects, and is widely dispersed in cultivated fields. The third form, V. alpestris, grows in the Alps, but is of lesser importance for our present discussion.

Anywhere throughout the central part of Europe V. tricolor and V. arvensis may be seen, each occupying its own locality. They may be considered as ranging among the most common native plants of the particular regions they inhabit. They vary in the color of the flowers, branching of the stems, in the foliage and other parts, but not to such an extent as to constitute distinct strains. They have been brought into cultivation by Jordan, Wittrock and others, but throughout Europe each of them constitutes a single type.

These types must be very old and constant, fluctuating always within the same distinct and narrow limits. No slow, gradual changes can have taken place. In different countries their various habitats are as old as the historical records, and probably many centuries older. They are quite independent of one another, the distance being in numerous cases far too great for the exchange of pollen or of seeds. If slow and gradual changes were the rule, the types could not have remained so uniform throughout the whole range of these two species. They would necessarily have split up into thousands and thousands of minor races, which would show their peculiar characteristics if tested by cultures in adjacent beds. This however, is not what happens. As a matter of fact V. tricolor and V. arvensis are widely distributed but wholly constant types.

Besides these, there occur distinct types in numerous localities. Some of them evidently have had time and opportunity to spread more or less widely and now occupy larger regions or even whole countries. Others are narrowly limited, being restricted to a single locality. Wittrock collected seeds or plants from as many localities as possible in different parts of Sweden and neighboring states and sowed them in his garden near Stockholm. He secured seeds from his plants, and grew from them a second, and in many cases a third generation in order to estimate the amount of variability. As a rule the forms introduced into his garden proved constant, notwithstanding the new and abnormal conditions under which they were propagated.

First of all we may mention three perennial forms called by him Viola tricolor ammotropha, V. tricolor coniophila and V. stenochila. The typical V. tricolor is an annual plant; sowing itself in summer and germinating soon afterwards. The young plants thrive throughout the latter part of the summer and during the fall, reaching an advanced stage of development of the branched stems before winter. Early in the spring the flowers begin to open, but after the ripening of the seeds the whole plant dies.

The three perennial species just mentioned develop in the same manner in the first year. During their flowering period, however, and afterwards, they produce new shoots from the lower parts of the stem. They prefer dry and sandy soils, often becoming covered with the sand that is blown on them by the winds. They are prepared for such seemingly adverse circumstances by the accumulation of food in the older stems and by the capacity of the new shoots to thrive on this food till they have become long enough to reach the light. V. tricolor ammotropha is native near Ystad in Sweden, and the other two forms on Gotland. All three have narrowly limited habitats.

The typical tricolored heartsease has remained annual in all its other subspecies. It may be divided into two types in the first place, V. tricolor genuina and V. tricolor versicolor. Both of them have a wide distribution and seem to be the prototypes from which the rarer forms must have been derived. Among these latter Wittrock describes seven local types, which proved to be constant in his pedigree-cultures. Some of them have produced other forms, related to them in the way of varieties. They all have nearly the same general habit and do not exhibit any marked differences in their growth, in the structure and branching of the stems, or in the character of their foliage. Differentiating points are to be found mainly in the colors and patterns of the flowers. The veins, which radiate from the centre of the corolla are branched in some and undivided in others; in one elementary species they are wholly lacking. The purple color may be absent, leaving the flowers of a pale or a deep yellow. Or the purple may be reddish or bluish. Of the petals all five may have the purple hue on their tips, or this attribute may be limited to the two upper ones. Contrasting with this wide variability is the stability of the yellow spot in the centre, which is always present and becomes inconspicuous only, when the whole petals are of the same hue. It is a general conception that colors and color-markings are liable to great variability and do not constitute reliable standards. But the cultures of Wittrock have proved the contrary, at least in the case of the violets. No pattern, however quaint, appears changeable, if one elementary species only is considered. Hundreds of plants from seeds from one locality may be grown, and all will exhibit exactly the same markings. Most of these forms are of very local occurrence. The most beautiful of all, the ornatissima, is found only in Jemtland, the aurobadia only in Sodermanland, the anopetala in other localities in the same country, the roseola near Stockholm, and the yellow lutescens_ in Finmarken.

The researches of Wittrock included only a small number of elementary species, but every one who has observed the violets in the central parts of Europe must be convinced that many dozens of constant forms of the typical Viola tricolor might easily be found and isolated.

We now come to the field pansy, the Viola arvensis, a very common weed in the grain-fields of central Europe. I have already mentioned its small corolla, surpassed by the lobes of the calyx and its capacity of self-fertilization. It has still other curious differentiating characters; the pollen grains, which are square in V. tricolor, are five-sided in V. arvensis. Some transgressive fluctuating variability may occur in both cases through the admixture of pollen-grains. Even three-angled pollen grains are seen sometimes. Other marks are observed in the form of the anthers and the spur.

There seem to be very many local subspecies of the field-pansy. Jordan has described some from the vicinity of Lyons, and Wittrock others from the northern parts of Europe. They diverge from their common prototype in nearly all attributes, the flowers not showing the essential differentiating characters as in the V. tricolor. Some have their flower-stalks erect, and in others the flowers are held nearly at right angles to the stem. V. pallescens is a small, almost unbranched species with small pale flowers. V. segetalis is a stouter species with two dark blue spots on the tips of the upper petals. V. agrestis is a tall and branched, hairy form. V. nemausensis attains a height of only 10 cm., has rounded leaves and long flower-stalks. Even the seeds afford characters which may be made use of in isolating the various species.

The above-mentioned elementary forms belong to the flora of southern France, and Wittrock has isolated and cultivated a number of others from the fields of Sweden. A species from Stockholm is called Viola patens; V. arvensis curtisepala occurs in Gotland, and V. arvensis striolata is a distinct form, which has appeared in his cultures without its true origin being ascertained.

The alpine violets comprise a more widespread type with some local elementary species derived exactly in the same way as the tricolored field pansies.

Summarizing the general result of this description we see that the original species Viola tricolor may be split up into larger and lesser groups of separate forms. These last prove to be constant in pedigree-cultures, and therefore are to be considered as really existent units. They are very numerous, comprising many dozens in each of the two larger subdivisions.

All systematic grouping of these forms, and their combination into subspecies and species rests on the comparative study of their characters. The result of such studies must necessarily depend on principles which underlie them. According to the choice of these principles, the construction of the groups will be found to be different. Wittrock trusts in the first place to morphologic characters, and considers the development as passing from the more simple to the more complex types. On the other hand the geographic distribution may be considered as an indication of the direction of evolution, the wide-spread forms being regarded as the common parents of the minor local species.

However, such considerations are only of secondary importance. It must be borne in mind that an ordinary systematic species may include many dozens of elementary forms, each of which remains constant and unchanged in successive generations, even if cultivated in the same garden and under similar external conditions.

Leaving the violets, we may take the vernal whitlow-grass or Draba verna for a second illustration. This little annual cruciferous plant is common in the fields of many parts of the United States, though originally introduced from Europe. It has small basal rosettes which develop during summer and winter, and produce numerous leafless flowering stems early in the spring. It is a native of central Europe and western Asia, and may be considered as one of the most common plants, occurring anywhere in immense numbers on sandy soils. Jordan was the first to point out that it is not the same throughout its entire range. Although a hasty survey does not reveal differences, they show themselves on closer inspection. De Bary, Thuret, Rosen and many others confirmed this result, and repeated the pedigree-cultures of Jordan. Every type is constant and remains unchanged in successive generations. The anthers open in the flower-buds and pollinate the stigmas before the expansion of the flowers, thus assuring self-fertilization. Moreover, these inconspicuous little flowers are only sparingly visited by insects. Dozens of subspecies may be cultivated in the same garden without any real danger of their intercrossing. They remain as pure as under perfect isolation.

It is very interesting to observe the aspect of such types, when growing near each other. Hundreds of rosettes exhibit one type, and are undoubtedly similar. The alternative group is distinguishable at first sight, though the differentiating marks are often so slight as to be traceable with difficulty. Two elementary species occur in Holland, one with narrow leaves in the western provinces and one with broader foliage in the northern parts. I have cultivated them side by side, and was as much struck with the uniformity within each group, as with the contrast between the two sets.

Nearly all organs show differences. The most marked are those of the leaves, which may be small or large, linear or elliptic or oblong and even rhomboidal in shape, more or less hairy with simple or with stellate branched hairs, and finally of a pure green or of a glaucous color. The petals are as a rule obcordate, but this type may be combined with others having more or less broad emarginations at the summit, and with differences in breadth which vary from almost linear types to others which touch along their margins. The pods are short and broad, or long and narrow, or varying in sundry other ways. All in all there are constant differences which are so great that it has been possible to distinguish and to describe large numbers of types.

Many of them have been tested as to their constancy from seed. Jordan made numerous cultures, some of which lasted ten or twelve years; Thuret has verified the assertion concerning their constancy by cultures extending over seven years in some instances; Villars and de Bary made numerous trials of shorter duration. All agree as to the main points. The local races are uniform and come true from seed; the variability of the species is not of a fluctuating, but of a polymorphous nature. A given elementary species keeps within its limits and cannot vary beyond them, but the whole group gives the impression of variability by its wide range of distinct, but nearly allied forms.

The geographic distribution of these elementary species of the whitlow-grass is quite distinct from that of the violets. Here predominant species are limited to restricted localities. Most of them occupy one or more departments of France, and in Holland two of them are spread over several provinces. An important number are native in the centre of Europe, and from the vicinity of Lyons, Jordan succeeded in establishing about fifty elementary species in his garden. In this region they are crowded together and not rarely two or even more quite distinct forms are observed to grow side by side on the same spot. Farther away from this center they are more widely dispersed, each holding its own in its habitat. In all, Jordan has distinguished about two hundred species of Draba verna from Europe and western Asia. Subsequent authors have added new types to the already existing number from time to time.

The constancy of these elementary species is directly proven by the experiments quoted above, and moreover it may be deduced from the uniformity of each type within its own domain. These are so large that most of the localities are practically isolated from one another, and must have been so for centuries. If the types were slowly changing such localities would often, though of course not always, exhibit slighter differences, and on the geographic limits of neighboring species intermediates would be found. Such however, are not on record. Hence the elementary species must be regarded as old and constant types.

The question naturally arises how these groups of nearly allied forms may originally have been produced. Granting a common origin for all of them, the changes may have been simultaneous or successive. According to the geographic distribution, the place of common origin must probably be sought in the southern part of central Europe, perhaps even in the vicinity of Lyons. Here we may assume that the old Draba verna has produced a host or a swarm of new types. Thence they must have spread over Europe, but whether in doing so they have remained constant, or whether some or many of them have repeatedly undergone specific mutations, is of course unknown.

The main fact is, that such a small species as Draba verna is not at all a uniform type, but comprises over two hundred well distinguished and constant forms.

It is readily granted that violets and whitlowgrasses are extreme instances of systematic variability. Such great numbers of elementary species are not often included in single species of the system. But the numbers are of secondary importance, and the fact that systematic species consist, as a rule, of more than one independent and constant subspecies, retains its almost universal validity.

In some cases the systematic species are manifest groups, sharply differentiated from one another. In other instances the groups of elementary forms as they are shown by direct observation, have been adjudged by many authors to be too large to constitute species. Hence the polymorphous genera, concerning the systematic subdivisions of which hardly two authors agree. Brambles and roses are widely known instances, but oaks, elms, apples, and pears, Mentha, Prunus, Vitis, Lactuca, Cucumis, Cucurbita and numerous others are in the same condition.

In some instances the existence of elementary species is so obvious, that they have been described by taxonomists as systematic varieties or even as good species. The primroses afford a widely known example. Linnaeus called them Primula veris, and recognized three types as pertaining to this species, but Jacquin and others have elevated these subspecies to the full rank of species. They now bear the names of Primula elatior with larger, P. officinalis with smaller flowers, and P. acaulis. In the last named the common flower-stalk is lacking and the flowers of the umbel seem to be borne in the arils of the basal leaves.

In other genera such nearly allied species are more or less universally recognized. Galium Mollugo has been divided into G. elatum with a long and weak stem, and G. erectum with shorter and erect stems; Cochlearia danica, anglica and officinalis are so nearly allied as to be hardly distinguishable. Sagina apetala and patula, Spergula media and salina and many other pairs of allied species have differentiating characters of the same value as those of the elementary species of Draba verna. Filago, Plantago, Carex, Ficaria and a long series of other genera afford proofs of the same close relation between smaller and larger groups of species. The European frost-weeds or Helianthemum include a group of species which are so closely allied, that ordinary botanical descriptions are not adequate to give any idea of their differentiating features. It is almost impossible to determine them by means of the common analytical keys. They have to be gathered from their various native localities and cultivated side by side in the garden to bring out their differences. Among the species of France, according to Jordan, Helianthemum polifolium, H. apenninum, H. pilosum and H. pulverulentum are of this character.

A species of cinquefoil, Potentilla Tormentilla, which is distinguished by its quaternate flowers, occurs in Holland in two distinct types, which have proved constant in my cultural experiments. One of them has, broad petals, meeting together at the edges, and constituting rounded saucer without breaks. The other has narrow petals, which are strikingly separated from one another and show the sepals between them. In the same manner bluebells vary in the size and shape of the corolla, which may be wide or narrow, bell-shaped or conical, with the tips turned downwards, sidewards or backwards.

As a rule all of the more striking elementary types have been described by local botanists under distinct specific names, while they are thrown together into the larger systematic species by other authors, who study the distribution of plants over larger portions of the world. Everything depends on the point of view taken. Large floras require large species. But the study of local floras yields the best results if the many forms of the region are distinguished and described as completely as possible. And the easiest way is to give to each of them a specific name. If two or more elementary species are united in the same district, they are often treated in this way, but if each region had its own type of some given species, commonly the part is taken for the whole, and the sundry forms are described under the same name, without further distinctions.

Of course these questions are all of a practical and conventional nature, but involve the different methods in which different authors deal with the same general fact. The fact is that systematic species are compound groups, exactly like the genera and that their real units can only be recognized by comparative experimental studies.

Though the evidence already given might be esteemed to be sufficient for our purpose, I should like to introduce a few more examples; two of them pertain to American plants.

The Ipecac spurge or Euphorbia Ipecacuanha occurs from Connecticut to Florida, mainly near the coast, preferring dry and sandy soil. It is often found by the roadsides. According to Britton and Brown's "Illustrated Flora" it is glabrous or pubescent, with several or many stems, ascending or nearly erect; with green or red leaves, which are wonderfully variable in outline, from linear to orbicular, mostly opposite, the upper sometimes whorled, the lower often alternate. The glands of the involucres are elliptic or oblong, and even the seeds vary in shape.

Such a wide range of variability evidently points to the existence of some minor types. Dr. John Harshberger has made a study of those which occur in the vicinity of Whitings in New Jersey. His types agree with the description given above. Others were gathered by him at Brown's Mills in the pinelands, New Jersey, where they grew in almost pure sand in the bright sunlight. He observed still other differentiating characters. The amount of seed produced and the time of flowering were variable to a remarkable degree.

Dr. Harshberger had the kindness to send me some dried specimens of the most interesting of these types. They show that the peculiarities are individual, and that each specimen has its own characters. It is very probable that a comparative experimental study will prove the existence of a large number of elementary species, differing in many points; they will probably also show differences in the amount of the active chemical substances, especially of emetine, which is usually recorded as present in about 1%, but which will undoubtedly be found in larger quantities in some, and in smaller quantities in other elementary species. In this way the close and careful distinction of the really existing units might perhaps prove of practical importance.

MacFarlane has studied the beach-plum or Prunus maritima, which is abundant along the coast regions of the Eastern States from Virginia to New Brunswick. It often covers areas from two to two hundred acres in extent, sometimes to the exclusion of other plants. It is most prolific on soft drifting sand near the sea or along the shore, where it may at times be washed with ocean-spray. The fruit usually become ripe about the middle of August, and show extreme variations in size, shape, color, taste, consistency and maturation period, indicating the existence of separate races or elementary species, with widely differing qualities. The earlier varieties begin to ripen from August 10 to 20, and a continuous supply can be had till September 10, while a few good varieties continue to ripen till September 20. But even late in October some other types are still found maturing their fruits.

Exact studies were made of fruit and stone variations, and their characteristics as to color, weight, size, shape and consistency were fully described. Similar variations have been observed, as is well known, in the cultivated plums. Fine blue-black fruits were seen on some shrubs and purplish or yellow fruits on others. Some exhibit a firmer texture and others a more watery pulp. Even the stones show differences which are suggestive of distinct races.

Recently Mr. Luther Burbank of Santa Rosa, California, has made use of the beach-plum to produce useful new varieties. He observed that it is a very hardy species, and never fails to bear, growing under the most trying conditions of dry and sandy, or of rocky and even of heavy soil. The fruits of the wild shrubs are utterly worthless for anything but preserving. But by means of crossing with other species and especially with the Japanese plums, the hardy qualities of the beach-plum have been united with the size, flavor and other valuable qualities of the fruit, and a group of new plums have been produced with bright colors, ovoid and globular forms which are never flattened and have no suture. The experiments were not finished, when I visited Mr. Burbank in July, 1904, and still more startling improvements were said to have been secured.

I may perhaps be allowed to avail myself of this opportunity to point out a practical side of the study of elementary species. This always appears whenever wild plants are subjected to cultivation, either in order to reproduce them as pure strains, or to cross them with other already cultivated species. The latter practice is as a rule made use of whenever a wild species is found to be in possession of some quality which is considered as desirable for the cultivated forms. In the case of the beach-plum it is the hardiness and the great abundance of fruits of the wild species which might profitably be combined with the recognized qualities of the ordinary plums. Now it is manifest, that in order to make crosses, distinct individual plants are to be chosen, and that the variability of the wild species may be of very great importance. Among the range of elementary species those should be used which not only possess the desired advantages in the highest degree, but which promise the best results in other respects or their earliest attainment. The fuller our knowledge of the elementary species constituting the systematic groups, the easier and the more reliable will be the choice for the breeder. Many Californian wild flowers with bright colors seem to consist of large numbers of constant elementary forms, as for instance, the lilies, godetias, eschscholtias and others. They have been brought into cultivation many times, but the minutest distinction of their elementary forms is required to attain the highest success.

In concluding, I will point out a very interesting difficulty, which in some cases impedes the clear understanding of elementary species. It is the lack of self-fertilization. It occurs in widely distant families, but has a special interest for us in two genera, which are generally known as very polymorphous groups.

One of them is the hawkweed or Hieracium, and the other is the dandelion or Taraxacum officinale. Hawkweeds are known as a genus in which the delimitation of the species is almost impossible, Thousands of forms may be cultivated side by side in botanical gardens, exhibiting slight but undoubted differentiating features, and reproduce themselves truly by seed. Descriptions were formerly difficult and so complicated that the ablest writers on this genus, Fries and Nageli are said not to have been able to recognize the separate species by the descriptions given by each other. Are these types to be considered as elementary species, or only as individual differences? The decision of course, would depend upon their behavior in cultures. Such tests have been made by various experimenters. In the dandelion the bracts of the involucre give the best characters. The inner ones may be linear or linear-lanceolate, with or without appendages below the tip; the outer ones may be similar and only shorter, or noticeably larger, erect, spreading or even reflexed, and the color of the involucre may be a pure green or glaucous; the leaves may be nearly entire or pinnatifid, or sinuate-dentate, or very deeply runcinate-pinnatifid, or even pinnately divided, the whole plant being more or less glabrous.

Raunkiaer, who has studied experimentally a dozen types from Denmark, found them constant, but observed that some of them have no pollen at all, while in others the pollen, though present, is impotent. It does not germinate on the stigma, cannot produce the ordinary tube, and hence has no fertilizing power. But the young ovaries do not need such fertilization. They are sufficient unto themselves. One may cut off all the flowers of a head before the opening of the anthers, and leave the ovaries untouched, and the head will ripen its seeds quite as well. The same thing occurs in the hawkweeds. Here, therefore, we have no fertilization and the extensive widening of the variability, which generally accompanies this process is, of course, wanting. Only partial or vegetative variability is present. Unfertilized eggs when developing into embryos are equivalent to buds, separated from the parent-plant and planted for themselves. They repeat both the specific and the individual characters of the parent. In the case of the hawkweed and the dandelion there is at present no means of distinguishing between these two contrasting causes of variability. But like the garden varieties which are always propagated in the vegetative way, their constancy and uniformity are only apparent and afford no real indication of hereditary qualities.

In addition to these and other exceptional cases, seed-cultures are henceforth to be considered as the sole means of recognizing the really existing systematic units of nature. All other groups, including systematic species and genera, are equally artificial or conventional. In other words we may state "that current misconceptions as to the extreme range of fluctuating variability of many native species have generally arisen from a failure to recognize the composite nature of the forms in question," as has been demonstrated by MacDougal in the case of the common evening-primrose, Oenothera biennis. "It is evident that to study the behavior of the characters of plants we must have them in their simplest combinations; to investigate the origin and movements of species we must deal with them singly and uncomplicated."