Part 72

POLLINATION. The flowers are adapted for insect-pollination; they secrete nectar at the base of the styles; individually they are rather small and insignificant, but yet are rendered conspicuous by being always crowded in many-flowered inflorescences. Protandry is common, sometimes to such an extent that the stamens have already fallen off before the styles begin to develop (Fig 539, 2). Insect visits are more frequent and numerous as the inflorescences are more conspicuous. The flowers as a rule are ☿, but ♂-flowers are often found interspersed among the others (Fig. 539), and the number of these becomes greater on the umbels developed at the latest period. A terminal flower, which differs from the others in form, and in Daucus carota often in colour also (purple), is sometimes found in the umbel. The nectar lies so exposed and flat that the flowers are principally visited by insects with short probosces, especially Diptera; bees are less frequent visitors, and butterflies rare.--1400 species (175 genera); especially from temperate climates in Europe, Asia, N. Am. About 68 species in this country.

USES. A few are cultivated as ornamental plants. They are, however, useful in medicine, and for culinary purposes on account of the essential oils and gum-resins which in many are formed in root, stem, and fruit. The FRUITS of the following are used: Carum carvi [+] (Caraway), Carum petroselinum (Parsley; also the leaves and root; its home is the Eastern Mediterranean); Fœniculum capillaceum [+] (Fennel; S. Europe); Pimpinella anisum [+] (Anise; E. Mediterranean); Coriandrum sativum [+] (Coriander; S. Eur.); Œnanthe phellandrium (Water Dropwort); Cuminum cyminum (Point Caraway; Africa; cultivated in S. Europe); Anethum graveolens (Dill). The LEAVES of the following are used as pot-herbs: Anthriscus cerefolium (Chervil); Myrrhis odorata (Sweet Cicely; Orient.); Conium maculatum [+] (the green portions; Hemlock). Besides Parsley, the ROOTS of the following are used: Carrot, Parsnip, Sium sisarum (Sugar-root; E. Asia); Chærophyllum bulbosum (Chervil-root); Levisticum officinale (foliage-shoots; S. Europe); Imperatoria ostruthium; Apium graveolens (Celery, the root in conjunction with the internodes); Pimpinella saxifraga and magna (Pimpinell); Archangelica (Angelica, the root of A. norvegica was formerly an article of food in Norway). Poisonous alkaloids are found in a few, such as Fool’s Parsley (Æthusa cynapium), Hemlock (Conium maculatum), Cow-bane (Cicuta virosa) and species of Œnanthe.--Gum-resin is extracted from various species: “Galbanum” from Ferula galbaniflua [+] and rubricalis [+] (Persia); Asafœtida from Ferula scorodosma [+] and F. narthex [+]; Ammoniac-gum from Dorema ammoniacum [+], all from Central and S. W. Asia. “Silphium” was an Umbelliferous plant which grew in ancient times in Cyrene, and from which the Romans extracted a valued condiment.

Family 25. =Hysterophyta.=

This family (with the exception of Aristolochiaceæ) includes only parasitic plants. Partly on this ground, and partly because they all have epigynous flowers, they are considered to belong to the youngest type (which is expressed in the name ὕστερος, the one that comes after). It is not certain to which of the preceding families they are most nearly allied. ~Again, it is a matter of doubt whether the Aristolochiaceæ are related to the others; they are by Engler united with Rafflesiaceæ into one family, Aristolochiales.~

Order 1. Aristolochiaceæ. The majority are perennial herbs or twining shrubs, whose stalked, simple, and generally more or less cordate or reniform leaves are borne in 2 rows and are exstipulate. The flowers are hermaphrodite, epigynous, regular or zygomorphic; perianth-leaves united, simple but most frequently petaloid and 3-merous; 6 or 12 (in Thottea as many as 36) stamens with extrorse anthers. The ovary is more or less completely 4–6-locular with ovules attached in the inner angles of the loculi (Fig. 540 kf). The style is short, and has a large, radiating stigma (Fig. 540 n). Fruit a capsule. Seeds rich in endosperm.

Asarum europæum. Each shoot has 2 reniform foliage-leaves, between which the terminal flower is borne (the rhizome becomes a sympodium by development of the bud in the axil of the upper foliage-leaf). The flower is regular and has a bell-shaped perianth with 3 outer valvate, and 3 inner small segments (which may be wanting). =12= (2 × 6) free, extrorse stamens, 6 carpels.--Aristolochia clematitis (Birth-wort) has an erect, unbranched stem, bearing many flowers in the leaf-axils, in a zig-zag row (accessory buds in a unipared scorpioid cyme). The flowers are zygomorphic (Fig. 540), formed by 3 alternating, 6-merous whorls. The perianth has a lower, much-distended part (k), succeeded by a narrow, bent tube (r), which passes over into an oblique, almost tongue-like projection (6 vascular bundles indicate that the number 6 is prevalent here, as in Asarum); =6= stamens (Fig. 540 a), with the dorsal portion turned upwards, are united with the short style to form a stylar column; they are placed quite beneath the 6 commissural stigmatic rays, which arch over them as short, thick lobes. ~Protogynous; POLLINATION is effected in Arist. clematitis by small flies; these enter the erect unfertilised flower through the tube (Fig. 540 A, l) without being prevented by the stiff, downwardly-turned hairs which line the tube and prevent their escape; they find the stigma (n) fully developed, and may pollinate it with the pollen they have brought with them. The stigmas then straighten and wither (B, n), the anthers open, and the flies may again be covered with pollen; but the hairs which blocked up the tube do not wither until the anthers have shed their pollen, and only then allow the imprisoned flies to escape and effect cross-pollination. Prior to pollination, the flowers stand erect, but after this has taken place they become pendulous, and the perianth soon withers.--A. sipho (Pipe-flower), another species, is a climber, and often grown in gardens; it has only one row of accessory buds in the leaf-axils.--200 species; chiefly in S. Am. OFFICINAL: the rhizome of Aristolochia serpentaria (N. Am.).~

Order 2. =Santalaceæ.= Parasites containing chlorophyll, which, by the help of peculiar organs of suction (haustoria) on their roots, live principally on the roots of other plants. Some are herbs, others under-shrubs. The regular, most frequently ☿-flowers have a simple perianth, which is gamophyllous, 3- or 5 partite with the segments valvate in the bud, and a corresponding number of stamens opposite the perianth-leaves. In the inferior ovary there is a free, centrally placed, often long and curved placenta with three ovules (one opposite each carpel); these are naked, or in any case have an extremely insignificant integument. Fruit a nut or drupe. Seed without testa. Endosperm fleshy. 225 species; chiefly in the Tropics.--Thesium, a native, is a herb with scattered, linear leaves and small 5-merous flowers (P5, A5, G3) in erect racemes; the subtending bracts are displaced on the flower-stalks. Fruit a nut.--Osyris (diœcious shrub; 3-merous flowers) is another European genus.--Santalum album, which grows in E. Ind., yields the valuable, scented Sandalwood, the oil of which is used medicinally.--Quinchamalium.

Myzodendron is a reduced form of the Santalaceæ; the ♂-flowers are without perianth; the perianth of the ♀-flower is 3-merous. About 7 species; S. Am.; parasitic on a Beech (Nothofagus). The fruit has 3 feathery brushes, alternating with the lobes of the stigma, which serve as flying organs and to attach the fruits to a branch (Fig. 541), the brushes twining round as soon as they come in contact with it. There is only 1 seed in the fruit, which germinates by a long, negatively heliotropic hypocotyl, and is attached by a radicle modified into an haustorium.

Order 3. =Loranthaceæ= (=Mistletoes=). Plants containing chlorophyll which are parasites on trees, and most frequently have opposite, simple, entire leaves and regular, epigynous, often unisexual, 2- or 3-merous flowers, with single or double perianth. Stamens equal in number and opposite to the perianth-leaves, free, or in varying degrees united to one another. The inferior ovary is constructed as in the Santalaceæ, the ovules being situated on a low, free, centrally-placed placenta, but the placenta and ovules unite with the wall of the ovary into one connected, parenchymatous mass, in which the embryo-sacs are imbedded. Only 1 (less frequently 2–3) of the 1–6 embryo-sacs is fertile. The number of the carpels however varies. The fruit is a 1-seeded berry, whose inner layer is changed into a tough slimy mass (bird-lime), which serves to attach the fruits to other plants.

The two groups, Loranthoideæ and Viscoideæ, are distinguished by the fact that the former has a distinct “calyculus,” i.e. an entire or lobed, or dentate swelling on the receptacle below the perianth. The majority of the Loranthoideæ have a petaloid perianth; in all the Viscoideæ, on the other hand, it is sepaloid.

The Mistletoe (Viscum album, Fig. 542) is a native, evergreen plant which may be found growing on almost any of our trees (sometimes on the Oak), and, like other Loranthaceæ, it produces swellings of the affected branches. ~Its spherical white berries (Fig. 542 A) enclose (1–) 2–3 green embryos; they are eaten by birds (especially Thrushes), and are partly sown with their excrement, partly struck or brushed off the branches of the trees, the seed being enclosed, at maturity, by viscin, i.e. “bird-lime.” The seeds may also germinate on the branches, without having first passed through the alimentary canal of the birds. On germination, the hypocotyl-axis first appears, as in Fig. 541, and bends towards the branch; the apex of the root then broadens, and forms at the end a disc-like haustorium, from the centre of which a root-like body grows through the bark into the wood, and ramifies between the bark and wood. Suckers are developed on the root like strands which are formed in this manner, without, however, having a rootcap; they are green, and penetrate the wood by the medullary rays (Fig. 542 C). Adventitious buds may also be developed from the root-like strands which break through the bark and emerge as young plants. The young stem quickly ceases its longitudinal growth, and lateral shoots are developed from the axils of its foliage-leaves. These and all following shoots have a similar structure; each of them bears a pair of scale-leaves (Fig. 542 A, a) and a pair of foliage-leaves (Fig. 542 A, b), and then terminates its growth, if it does not produce an inflorescence; new lateral shoots proceed from the axils of the foliage-leaves, and the branching, in consequence, is extremely regular and falsely dichotomous. Only one internode (shoot-generation) is formed each year, so that each fork indicates one year. The foliage-leaves fall off in the second year. The inflorescence is a 3(-5)-flowered dichasium (Fig. 542 A, m is the central flower, n the lateral). The plants are diœcious; the ♂-flower as a rule is 2-merous: perianth 2 + 2, each leaf of which bears on its inner side 6–20 pollen-sacs, each of which opens by a pore; this relationship may be considered to have arisen from the union of the perianth-leaves with the multilocular stamens (2 + 2) placed opposite them. The ♀-flowers always have Pr 2 + 2, G2.--Loranthus is also found in Europe (it has a 3-merous flower), especially in the central and south-eastern districts, on Quercus cerris and Q. pubescens; but the great majority of the 520 species grow in the Tropics on trees which they ornament with their often brightly-coloured flowers, and ultimately kill when present in too great numbers. The pollination in the numerous Loranthaceæ with unisexual flowers, is effected by the wind. In Viscum album this takes place in autumn, the actual fertilisation in the following spring, and the maturity in November or December; in the succeeding month of May the berry is ready to germinate, and falls off.~

USES. Birdlime from Viscum album.

Order 4. =Rafflesiaceæ= and Order 5. =Balanophoraceæ=. These orders comprise root-parasites, almost entirely devoid of chlorophyll; they are reddish or yellow, without foliage-leaves (Fig. 543). As far as our knowledge of these rare tropical plants extends, they have thalloid organs of vegetation resembling the root-like strands of Viscum, or they are filamentous and branched like Fungus-hyphæ; they live in and on the tissues of the host-plant, from which their flowering-shoots, often of mushroom-like form, are subsequently developed (Fig. 543). In order to unfold they must often break through the tissues of the host-plant.

Of the RAFFLESIACEÆ, Cytinus hypocistus is found in S. Europe living on roots of Cistus-plants and to some extent resembling Monotropa (Fig. 543). Rafflesia is the best known; it lives on roots of Cissus-species (belonging to the Ampelidaceæ) in Java; its yellowish-red, stinking flowers attain a gigantic size (one metre or more in diameter), and are borne almost directly on the roots of the host-plant. Besides these there are other genera: Brugmansia, Pilostyles, Hydnora.--To BALANOPHORACEÆ (Fig. 543) belong: Balanophora, Langsdorffia, Scybalium, Sarcophyte, Helosis, etc., and in S. Europe, Cynomorium coccineum.

Sub-Class 2. =Sympetalæ.=

The characters which separate this from the first Sub-class, the Choripetalæ, have been described on page 336. They consist in the following: the flower is always verticillate, generally with =5= sepals, =5= petals, =5= stamens, and =2= carpels (in the median plane), the calyx is generally persistent and gamosepalous, the corolla is gamopetalous and united to the stamens, which are therefore adnate to it, the ovules have only one thick integument and a small nucellus. (The exceptions are noted later.)

This Sub-class is no doubt more recent than the Choripetalæ; it is also peculiar in including fewer trees and shrubby forms than the latter.

The Sympetalæ may be separated into 2 sections:--

=A.= PENTACYCLICÆ (FIVE-WHORLED). The flowers in this section have 5 whorls equal in number, namely, 2 staminal whorls in addition to the calyx, corolla, and carpels; in some instances, one of the staminal whorls is rudimentary or entirely suppressed, but in this case it is frequently the sepal-stamens which are suppressed, and the whorl which is present stands opposite the petals. The flowers are regular. The number of carpels equals that of the sepals, but in one of the orders (Bicornes) they are opposite the petals (the flower being obdiplostemonous); in the other two orders (Primulinæ and Diospyrinæ) they are placed opposite the sepals (the flower being diplostemonous). This section is the most closely allied to the Choripetalæ, since the petals may sometimes be found entirely free, and the stamens inserted directly on the receptacle (Ericaceæ); ovules with two integuments are also found. ~It is very doubtful, whether the orders included under this head have any relationship with the other Sympetalæ. They appear in any case to represent older types.~

=B.= TETRACYCLICÆ (FOUR-WHORLED). The flowers have only 4 whorls, namely, beside sepals, petals, and carpels, only one whorl of stamens, which alternates with the petals; there is no trace of the second staminal whorl, and when the number of carpels is the same as that of the preceding whorls (“isomerous”) they alternate with the stamens; but in most cases there are 2 carpels placed in the median plane (see the diagrams, e.g. Figs. 559, 567, 583, 590, etc.). This section is the largest, and the one which shows the characteristics of the Sympetalæ best. Very irregular flowers are met with.

The following families belong to the =Pentacyclicæ=: 26, Bicornes; 27, Diospyrinæ; 28, Primulinæ.

The remaining families belonging to the =Tetracyclicæ= are:--

=a.= HYPOGYNOUS flowers (with a few exceptions): 29, Tubifloræ; 30, Personatæ; 31, Nuculiferæ; 32, Contortæ.

=b.= EPIGYNOUS flowers: 33, Rubiales; 34, Dipsacales; 35, Campanulinæ; 36, Aggregatæ. The ovaries and ovules in the last family are always reduced to one; and at the same time the fruits become nuts, and the flowers are united into crowded inflorescences.

A. Pentacyclicæ.

Family 26. =Bicornes.=

This family is chiefly composed of shrubs, less frequently of small trees, or perennial herbs; their leaves are undivided, most frequently evergreen, stiff and leathery, and always without stipules. The flowers are ☿ and regular, rarely slightly zygomorphic, most frequently obdiplostemonous, and 4- or 5-merous through all the 5 whorls. The stamens are attached to the receptacle, and as a rule are quite free from the petals, an attachment which is very rare among the Gamopetalæ. They have a simple gynœceum with one undivided style, a commissural stigma, and a multilocular ovary, whose axile placentæ project considerably into the loculi, and bear a large number of ovules. ~The placentæ are sometimes not united, and in consequence, the ovary is 1-locular with incomplete partition-walls, e.g. Pyrola, Monotropa.~ Embryo straight, with endosperm. The carpels are placed opposite the petals.

The diagram is generally Sn, Pn, An + n, Gn, in which n is 4 or 5. To this may be added, that the corolla is in most cases gamopetalous, but in some (especially Pyrolaceæ) perfectly polypetalous; and that the anthers usually open by pores, and often have two horn-like appendages (hence the name “Bicornes”) (Figs. 545, 546); frequently the two halves of the anther are also widely separated from each other at the upper end, so that the pores are placed each one at the end of its own tube (Fig. 546); the pollen-grains in the majority are united into tetrads (Fig. 542 D).--The flowers, as a rule, are pendulous and borne in racemes, coloured (red or white), but odourless. When the fruit is a capsule, the placenta with the seeds attached persists as a central column. A mycorhiza occurs on many.