Part 30

=3.= NEOTTIEÆ. The majority are terrestrial Orchids with creeping, sympodial rhizomes; the blades of the leaves are not detached from the stem at joints, and have convolute vernation. The anthers do not drop off, but persist in the withered condition; their _apex_ is brought in contact with the rostellum (acrotonous Orchids). The pollen-grains are united in _tetrads_, which, however, often hang loosely together in pollinia, attached to a sticky part of the rostellum (“adhesive disc”), so that they adhere to the insects, and are by them transferred to the stigmas. _Spiranthes. Listera_; _Neottia_. ~_N. nidus-avis_ (Bird’s-nest) is brown (it has little chlorophyll) in colour, has no foliage-leaves, and lives mainly as a saprophyte; the rhizome is studded with unbranched, fleshy roots which may form buds at their extremities.~--_Vanilla_ climbs by aerial roots. The fruit is fleshy and hardly opens, or does so irregularly.--_Epipactis_, _Cephalanthera_.--_Epipogon_ and _Limodorum_ are saprophytes without chlorophyll.

=4.= OPHRYDEÆ. Anthers 2-locular, not falling off, on a very short column. The anther is united at _its base_ with the rostellum (_basitonous_ Orchids, Fig. 320 _A_, _B_), while in all other Orchids it is connected at the apex (acrotonous Orchids). The pollen-grains in each loculus are united into small “masses” (massulæ), each of which corresponds to a pollen-mother-cell in the anther, and which hang together by elastic threads (Fig. 320 _C_, _E_). Each pollinium is attached at the base by a stalk (caudicle) to an adhesive disc, formed by the modified stigma (rostellum), and is easily liberated from it (Fig. 320 _C_, _D_, _F_). The pollinium, which is formed in an anther-loculus, together with its caudicle and adhesive disc, is termed “pollinarium” (Fig. 320 _C_).--All Ophrydeæ are terrestrial with _tuberous roots_, two of which are present in the flowering period, an older one (from the preceding year) containing the nourishment for the flowering-shoot of the year, and a young one which is intended to contain the reserve material for the following year. Inflorescence terminal.

_Orchis._ The lip has a spur; each of the club-like pollinia is attached to its own adhesive disc, the discs being enclosed in a common pouch formed by the rostellum (Fig. 320 _C_, _D_). ~Tubers ovate, undivided: _O. morio_, _mascula_; tubers palmate: _O. incarnata_, _maculata_, _majalis_.~--_Ophrys_; no spur, the two adhesive discs are each enclosed in a separate pouch (Fig. 320 _F_).--_Anacamptis_ and _Serapias_ have one adhesive disc.--_Habenaria_, _Gymnadenia_, _Platanthera_, _Herminium_, _Nigritella_, _Cœloglossum_, etc., have naked adhesive discs (no rostellum).

=5.= EPIDENDREÆ. Acrotonous Orchids with deciduous anthers (except _Malaxis_); 2-8 wax-like pollinia, with or without caudicles; generally no adhesive discs. _Malaxis_ (the flower is twisted through a complete circle, causing the labellum to be turned upwards), _Sturmia_ and _Corallorhiza_[32] (Coral-root); the latter has a creeping, coral-like rhizome _without roots, and is destitute of chlorophyll_ except in the ovary. The other two somewhat resemble the tropical Orchids in having the lower internodes of the axis of the inflorescence tuberous. _Liparis_; _Calypso_. Most of the genera are tropical epiphytes and many have aerial, green tubers formed from one or more stem-internodes; _Dendrobium_, _Eria_, _Phaius_, _Bletia_, _Epidendrum_, _Cattleya_, _Lælia_, _Pleurothallis_, _Restrepia_, _Masdevallia_, _Bulbophyllum_, etc.

=6.= VANDEÆ. These resemble the preceding but have only 2 wax-like pollinia in each anther, which are attached by a caudicle to the adhesive disc of the rostellum. Nearly all are tropical epiphytes. _Stanhopea_, _Catasetum_, _Maxillaria_, _Oncidium_, _Vanda_, _Polystachya_, etc.

6,000 (10,000?) species. The majority live in the Tropics and occur, especially, as epiphytes on trees or in the crevices of rocks, to which they are attached by aerial roots. These _aerial roots_, like those of Araceæ, are covered by several layers of spirally-thickened cells (tracheides) which contain air and form the velamen--an apparatus to absorb moisture from the air. The roots have a white appearance when the cells are filled with air, which changes to a greenish hue when they are filled with water, the chlorophyll then shining through. They generally have horizontal rhizomes; the ascending shoots, which bear the foliage-leaves, may vary, but they very often swell and assume the form of a tuber, which persists for several years fresh and green after the leaves have fallen off (Fig. 321). _Vanilla_ is an exception (see above). Our Orchids are all terrestrial (or marsh-plants); the largest number of species is found in calcareous soils.

POLLINATION takes place principally by means of insects, but self-pollination occurs in some. The lip serves as a landing-stage for the insect visitors, which, on sucking the honey, cause the adhesive discs, with the pollinia attached to them, to adhere to their bodies (generally to the probosces) and so carry them away to other flowers. In some species parts of the flower are sensitive or irritable, which has some connection with the pollination. Without doubt there are a great many biological differences which are closely connected with the infinite multiplicity of forms; Darwin (1862) has already shown an enormous variety, never even dreamt of before, in the European species. The genus _Catasetum_ has ♂-♀-and ☿-plants with flowers of such different appearances that they have been classed in various genera (_Myanthus_, _Monacanthus_). _Platanthera_ is pollinated by hawk-moths; _Ophrys_, by flies; _Epipactis latifolia_, by wasps; _Orchis_, by bees, especially humble-bees, etc.

The DISTRIBUTION OF SEEDS is effected by the wind, the seeds being so exceedingly small and light. Many species moreover have peculiar, elater-like, fine, hygroscopic hairs in the ovary, which eject the seeds in a manner similar to the elaters of the Liverworts.

The USES are few, mostly as ornamental plants in conservatories. The tubers of several _Orchis_-species are OFFICINAL; they contain starch and mucilage and are used us “salep.” The fruits of _Vanilla planifolia_ are used as condiments and differ from other _Orchid_-fruits in being rather fleshy and in dehiscing irregularly; the seeds are very small, shining and black.

Class II. =Dicotyledones.=

In this class THE EMBRYO has 2 seed-leaves, a rule from which there are few exceptions (_e.g. Ficaria_, _Cyclamen_, _Pinguicula_, certain species of _Corydalis_, with only 1; and a few, mostly parasitic forms, _e.g. Monotropa_, _Orobanche_, _Pyrola_, entirely without cotyledons). On germination the cotyledons nearly always raise themselves above the ground as green, assimilating leaves and are then termed aerial or epigean, in contradistinction to the underground or hypogean which are always buried. The structure of the seed varies (endospermous or exendospermous); the embryo may be straight or curved. In many instances the primary root grows as a vigorous tap-root, with weaker branches arising acropetally (in annuals, biennials, many perennials, especially woody plants); but in a large number of herbaceous perennials, which have rhizomes, the root behaves very much as in the Monocotyledons. The roots generally increase in thickness by means of a cambium.

THE STEM, when seen in transverse section, has its vascular bundles arranged in a ring; in reality, however, they form a kind of cylindrical network in the stem; the bundles are open, and thickening takes place by means of a cambium; annual rings are formed in the perennial stems. There is a rich and very varied form of _branching_. The two first leaves of a shoot (fore-leaves) are placed nearly always to the right and to the left; the same arrangement is found in the two first leaves developed on the flower-stalk, and these are, as a rule, the only two; they are found below the calyx and are usually termed the “_bracteoles_.” It has become customary to indicate the bracteoles by the letters α and β, according to their sequence of growth, and in that sense these letters will be employed in the following diagrams.

THE ARRANGEMENT OF THE LEAVES varies very much; there is also a great variety of shapes in the leaves and their venation, but the linear leaves, with parallel venation, so frequent in the Monocotyledons, are seldom met with, as also the large sheaths (though the sheath is well developed in the Umbelliferous plants); stipules occur much more frequently.

THE FLOWER is most commonly cyclic, but acyclic or hemicyclic forms also occur. The type which may be taken as a basis consists in the majority of instances, as in the Monocotyledons, of 5 whorls, of which the 4 outer ones (calyx, corolla, and the 2 whorls of stamens) are most frequently 4 or 5 in number and placed in regular alternation, whilst the innermost one (the carpels) has generally fewer members, probably on account of space (Figs. 360, 361, 421, 429, 487, etc.). Trimerous (Figs. 384, 387, etc.) flowers, or those in which the members of the flower are in threes or a multiple of three, also occur, as well as dimerous flowers; other numbers are rare. It is of the greatest importance in connection with the relative position of the members of the flower to the axis and bract (orientation), whether the bracteoles are typically present (even though they may not be developed), or are typically absent. If there are 2 bracteoles present, then their position in a pentamerous flower is often as follows: the first sepal turns obliquely forward, the second is posterior and median, the third obliquely forward, the fourth and fifth obliquely backward; quincuncial æstivation is often found in these buds (Figs. 360, 429, 471, 475, 584). The first and third leaves, in the following chapters, are most frequently alluded to as the “anterior,” the fourth and fifth as the “lateral” leaves. The _reversed_ arrangement, with the median sepal in the front, occurs for instance in _Papilionaceæ_ (Fig. 511), _Lobeliaceæ_ (Fig. 594), _Rhodoracecæ_. If any bracteoles are present below a tetramerous flower, the relation is generally that 2 sepals (the first ones) stand in the median plane, the two next ones transversely (Fig. 393), and the corolla then adopts a diagonal position (Fig. 397); but a diagonal position of the calyx generally shows that the flower is not, strictly speaking, tetramerous, as in _Plantago_ (Fig. 567), _Veronica_ (Fig. 559 _C_) and others.

If the bracteoles are _not_ typically present, then the position of the sepals is changed accordingly, and the two outer sepals endeavour to assume the position which the bracteoles would otherwise have occupied, _e.g._ in _Primula_ (Fig. 547). Other positions are also found when the number of bracteoles is more or less than two.

The leaves which follow the sepals occupy definite positions with regard to them, which we may consider later. An arrangement must, however, be mentioned here; when the flower is “_diplostemonous_” that is, has two whorls of stamens (thus, Sn, Pn, An + n), these may be arranged in two ways. _Either_ the first-formed whorl of stamens, which are termed the “calyx-stamens,” stands directly in front of the sepals (that is “episepalous”), and is the _outermost_ whorl, and in this case a regular alternation takes place between sepals, petals and the two whorls of stamens, which is also continued into the carpels if their number is the same as that of the other whorls: the carpels are then placed opposite the sepals (Fig. 278) and the flower is _isomerous_ and Gn should be added to the formula above. _Or_, the calyx-stamens form the _innermost_ whorl, and the corolla-stamens, which are subsequently formed (“epipetalous” stamens), stand _outside_ these (Figs. 360, 429); if the number of carpels is the same as that of the preceding whorls, they are often placed _right in front_ of the petals and the corolla-stamens. The first-mentioned arrangement is termed _Diplostemonous_, and the second _Obdiplostemonous_. ~Both arrangements may be found in one and the same order, _e.g._ Caryophyllaceæ. The size and relation of the members of the flowers, and also the contact with other members in the early stages of their development, play an important part in determining the arrangement.~

The great number of structural arrangements found in this enormously large class, may, as is the case in the Monocotyledons, be further varied by _suppression and division_ of certain leaves (especially the stamens). Instances of this will occur in the following (Figs. 559, 568.--426, 441, 445, etc.).

The Dicotyledons were formerly divided into 3 sub-classes: Apetalæ (those without corolla), Sympetalæ or Gamopetalæ (those with the petals united), and Choripetalæ or Polypetalæ (the petals not united). This division has now been abandoned because it has been proved that the Apetalæ were merely reduced or incomplete forms of the Choripetalæ, and they have therefore been distributed among the various families of the latter sub-class.

With regard to the Sympetalæ (or Gamopetalæ) it may be stated that they form to a very great extent a closely connected and natural group, having in common not only the character that the corolla is gamopetalous and the stamens united with it (this being also found in the Choripetalæ), but also a great many others (such as persistent calyx, cyclic flowers with the formula S5, P5, A5 and as a rule G2, the two carpels being united to form the ovary; seeds with a thick integument and a very small nucellus). They are therefore considered as an independent sub-class, and must be placed at the close of the system of classification as the forms which presumably have arisen the latest. In the future systems of classification this arrangement will very probably be changed, and the first families of the Sympetalæ, the Bicornes and others will for instance be to a certain extent united with the families or orders of the Choripetalæ. The Sympetalæ may certainly be considered as the youngest types, the strongly pronounced metamorphosis supporting this theory, as also the formation of the integument of the ovule, the one thick integument being undoubtedly derived from the coalescence of two--a holochlamydeous ovule, etc.

The Apetalæ and Choripetalæ are united into one sub-class. The leaves of the perianth in this case are, as a rule, free from each other, the structure of the flowers presents many differences, and the ovules have as a rule 2 integuments and a large nucellus. Considerable uncertainty still prevails regarding the arrangement and the relationship of the individual families of the Choripetalæ, and some of the following families are hardly quite natural; but the best arrangement arrived at so far has been adopted here.

At the beginning of the book a review of the orders of the Dicotyledons will be found.

Sub-Class 1. =Choripetalæ. Petals free.=

Family 1. =Salicifloræ.=

Trees and shrubs, which, in the structure of the vegetative shoot and the catkin-like inflorescences, resemble the Quercifloræ, but the structure of the flower differs so much from them, that the only order brought under this heading--_Salicaceæ_--well deserves to be separated and to form a family of its own, the nearest relatives of which are still doubtful. ~As Juglandaceæ and Myricaceæ also deserve to be placed in a special family, the name _Amentaceæ_ (_Catkin-bearers_), hitherto applied to all of these plants, cannot be retained as the name of a family.~

There is only one order.

Order. =Salicaceæ= (=Willows=). Trees with simple, scattered, _stipulate leaves_. _Diœcious_. The flowers are arranged in _simple inflorescences_ (spikes or racemes) which are termed catkins, and which fall off as a whole after flowering (♂) or after the ripening of the fruit (♀) (Fig. 322). The perianth is very imperfect[33] or wanting, particularly in _Salix_ (Fig. 323 _o_); the ♂-flower with 2–several stamens and without any trace of a carpel (_a_, _b_, _c_): the ♀-flower has a free bicarpellate ovary, _unilocular_, and formed from 2 lateral carpels with 2 _parietal_ (_median_) _placentæ_ and generally ∞ ovules; the style divides into two stigmas (_d_, _e_, _f_). The fruit is a two-valved _capsule_ and the very small seeds bear a _tuft of hairs_ at the base. _Endosperm absent._--~The catkins are situated on dwarf-branches, which in some species often develop before the leaves and bear at their base only scale-leaves; in others foliage-leaves are borne beneath the catkins. The vegetative bud commences with 2 bud-scales which are united on the anterior side into a scale. The capsule opens by the dorsal suture. The seed-hairs spring from the funicle.~

_Salix_ (Willow) has short-stalked, most frequently lanceolate leaves and erect catkins with undivided bracts (Fig. 322). The flowers are naked; 1 (_o_ in _a-f_) or 2 yellowish glands situated in the median line. In the ♂-flower generally two stamens, situated laterally like the carpels in the ♀-flower. ~Various forms are seen in Fig. 323.--The terminal bud of the branches often aborts regularly, the uppermost lateral bud taking its place.~

_Populus_ (Aspen, Poplar) has long-stalked, more or less round or cordate leaves with drawn-out apex; catkin pendulous; lobed bracts; perianth cup-like with oblique edge; stamens usually numerous; stigmas often divided.--~_P. tremula_ (Aspen) has received its name from the tremor of the leaves: _cf._ “to shake like an aspen leaf.”~

POLLINATION. The Poplars are wind-pollinated. The Willows have sticky pollen and are pollinated by insects. The catkins of the Willows, especially the ♂, are more conspicuous, from the numerous, closely-packed, yellow flowers, rich in honey and pollen. The catkins often appear before the foliage and so are much more easily seen, whilst at this time of the year the number of competing honey-flowers is smaller, and the insect visits consequently more numerous. On many catkins of the Willow the flowers open earliest on the side which is turned towards the sun and in descending order, _i.e._ the upper flowers develop before the lower ones. Hybrids frequently appear.

There are about 180 species existing in the northern, cold and temperate latitudes. Some in the Polar regions are scarcely more than an inch in height, and have a creeping rhizome (_Salix herbacea_, _polaris_, _reticulata_). Fossil forms are found in the Tertiary and perhaps also in the Upper Cretaceous.

USES. Principally for ornamental trees, as they grow very quickly and are easily propagated by cuttings, _S. babylonica_, Weeping Willow; _S. purpurea_; _Populus alba_, Silver Poplar; _P. pyramidalis_, Pyramid Poplar--a form of _P. nigra_; _P. monilifera_, Canadian Poplar. The wood is very poor and little used; the branches of many Willows are cultivated for basket-making, etc. The wood of the Aspen is used for matches. The bark contains tannin and, in many Willows, a very bitter extract, _Salicin_ (_S. pentandra_, _fragilis_). Salicylic acid (officinal) is obtained from _Salix_. Balsam is extracted from the buds of many Poplars, especially when the leaves are shooting.

Family 2. =Casuarinifloræ.=

Trees with verticillate, scale-like leaves forming sheaths at the nodes. Monœcious. Flowers unisexual. ♂-flowers in catkins; ♀ in short spikes. _Pollen-tube entering the ovule at the chalaza_, and not through the micropyle. Ovary 1-seeded, unilocular. Carpels uniting into a multiple fruit. Only one order.

Order. =Casuarinaceæ.= Trees (30 species), from Australia and certain parts of S.E. Asia, with peculiar, equisetum-like appearance. The leaves are verticillate, scale-like and united into sheaths. The internodes are furrowed. Branching verticillate. The unisexual flowers are situated in catkins or short spikes. The ♂-flower has a central stamen, surrounded by 2 median, scale-like perianth-leaves and 2 lateral bracteoles. The ♀-flower has a 1-chambered ovary (2 ascending, orthotropous ovules), no perianth, but 2 large, lateral bracteoles which finally become woody and form two valves, between which the nut-like fruit is situated. The multiple-fruits therefore resemble small cones.--_Casuarina equisetifolia_, cultivated, gives “iron-wood.”

[The Casuarinas differ from the ordinary Dicotyledons in many important respects which may be briefly summarised thus:--The bicarpellate ♀-flower has a well-pronounced stylar-cylinder terminated by two stigmas, but the cavity of the ovary closes very soon after its formation, and in it are developed two parietal ovules; these are united by a bridge of cellulose to the stylar-cylinder or summit of the ovary, and hence the ovules are connected with the walls of the ovary by the bridge (above), as well as by the funicle (below). The archespore is developed from the hypodermal cells at the summit of the nucellus, two primordial mother-cells are first formed and from these by tangential divisions a central cylindrical mass of cells (sporogenous-tissue) is produced which is surrounded by tapetal cells. The cells of the sporogenous tissue correspond to the mother-cells of the embryo-sac of other Angiosperms; they divide transversely and from 16–20 macrospores are formed together with inactive cells which are not crushed together as in the case of other Phanerogams. The sexual apparatus is developed from a single cell, but the number of cells composing this apparatus is subject to variation, the oosphere being accompanied by one or two neighbouring cells which resemble canal-cells rather than synergidæ. The sexual apparatus is found in the majority of the macrospores, but in most of these it remains as a number of naked cells; while in the fertile macrospores the cells are invested by walls of cellulose (usually only one fertile macrospore is found in each ovule). Antipodal cells are never developed. The macrospores elongate considerably towards the chalaza, into which some penetrate. The pollen-tube traverses the stylar-cylinder and enters the ovules at the chalaza, its passage through the tissue of the nucellus being assisted by the prolongation of the macrospores. About the centre of the nucellus the pollen-tube is ruptured; the apical portion which alone takes part in the fertilisation being firmly attached to the macrospore. Although the actual impregnation has not been observed, Treub considers that the endosperm begins to be formed before fertilisation.]

Family 3. =Quercifloræ.=