Part 24

_Taxodium distichum_ (the North American “Swamp Cypress”) has annual dwarf-branches, with distichous leaves, and cone-like “pneumathodia.” In the Tertiary period it was very common in the Polar regions. _Sequoia (Wellingtonia) gigantea_ is the famous Californian Giant-Fir, or Mammoth-Tree, which attains a height of 300 feet, a diameter of 36 feet, and is said to live for 1,500 years. _Cryptomeria japonica_ (Japan, China) has the least adnate ovuliferous scales; _Glyptostrobus_ (China); _Arthrotaxis_ (Tasmania); _Sciadopitys verticillata_ (the only species in Japan) has, like _Pinus_, scale-like leaves on the long-branches, of which those which are situated at the apex of the annual shoots support “double needles,” _i.e._ _dwarf-branches_ similar to the two-leaved dwarf-branches in _Pinus_, but without bud-scales, and with the two leaves fused together at the edges into one needle, which turns its upper surface away from the long-branch.

Order 4. =Cupressaceæ= (=Cypresses=). _The leaves are opposite or verticillate_, sometimes acicular, but most frequently scale-like (Fig. 270). In the species with scale-like leaves, the seedlings often commence with acicular leaves (Fig. 272), and branches are sometimes found on the older plants which revert to this form, seeming to indicate that the acicular leaf was the original form (atavism). The so-called “_Retinospora_” species are seedling-forms of _Biota_, _Thuja_, _Chamæcyparis_, which have been propagated by cuttings, and retain the seedling-form. The flowers are monœcious or diœcious. The male flowers are short, and have shield-like stamens, bearing most frequently several pollen-sacs. The cover-scales and ovuliferous scales are entirely fused together and form _undivided_ cone-scales, _opposite or whorled_; _the ovuliferous scales_ have slight projections near _the base_ on which 1–2–several _erect ovules_ are developed (Fig. 274). Most frequently 2 cotyledons.--_Evergreen_ trees and shrubs.

_Juniperus_ (Juniper). _Diœcious._ The cone-scales become fleshy and fuse together to form most frequently a 1–3 seeded “berry-cone.” ~_J. communis_ (Common Juniper) has acicular leaves, borne in whorls of three, and the “berry-cone” is formed by a trimerous whorl of cone-scales (Fig. 273). _J. sabina_ and _J. virginiana_ have “berry-cones” formed from several dimerous whorls of cone-scales; the leaves are connate and opposite, needle-and scale-like leaves are found on the same plant.~

_Cupressus_ (Cypress). _Monœcious._ The cones are spherical; the cone-scales shield-like, generally five-cornered and woody (Fig. 270), each having many seeds. The leaves are scale-like.--_Thuja. Monœcious._ Cones oblong. The cone-scales are dry, as in the Cypress, but leathery and imbricate, and not shield-like; each cone-scale bears 2–3 seeds. The leaves are most frequently dimorphic; those leaves which are situated on the edges of the flat branches are compressed, and only these bear buds, which are developed with great regularity, generally alternately, on both sides of the branch; those which are situated on the flattened surfaces are pressed flat and broad, and never bear branches (Fig. 271). Along the central line of each leaf there is a resin-canal (Fig. 271).--~_Chamæcyparis_, _Callitris_, _Libocedrus_, _Thujopsis_ (1 species: _T. dolabrata_; in Japan).~

OFFICINAL. _Juniperus sabina_ from Central and South of Europe (the young branches yield an essential oil). The wood of _J. communis_ is used in the production of an essential oil, and _J. oxycedrus_ in the production of empyreumatic oil. The “berry-cone” of _J. communis_ is officinal, and is also used for gin.--The wood of _J. virginiana_ (N. Am.) is known as red cedar, and is used for lead-pencils. Sandarack resin is obtained from _Callitris quadrivalvis_ (N.W. Africa).

THE FOLLOWING ARE CULTIVATED IN GARDENS:--_Thuja occidentalis_ (Arbor vitæ) (N. Am.), and _orientalis_ (China, Japan); _Juniperus sabina_ and _virginiana_; _Thujopsis dolabrata_ (Japan); _Cupressus lawsoniana_ (California), _C. sempervirens_ (S. Eur., W. Asia), and other species, are grown especially in conservatories, and in Southern Europe particularly in cemeteries.--The _Retinospora_ species which are so often planted, do not belong to an independent genus, but are obtained from cuttings, taken from seedling-plants with acicular leaves (see page 267).

Class III. =Gneteæ.=

This class, independent of extinct forms, comprises the most highly developed of the Gymnosperms, partly from the circumstance that a perianth of 2–4 members encloses the _terminally placed ovule_, which is provided with one, or (in _Gnetum_) two, integuments, and partly owing to the fact that the wood has true vessels. There is only one order.

Order. =Gnetaceæ.= The three known genera differ very much in appearance. _Welwitschia mirabilis_ (from the deserts of South Western Africa) is the oldest (?) genus now living. It resembles a giant radish, in that the hypocotyl is the only part of the main axis of the stem which becomes developed. It attains a circumference of upwards of four metres with a length of 1/2½-⅔ of a metre. It bears _only_ two oblong, leathery leaves (Fig. 275) which are torn into segments at the apex and lie on the surface of the soil; these are the two first foliage-leaves which succeed the cotyledons, and they are remarkable for their enormous length (upwards of two metres) as well as for their long duration, living as long as the plant itself. In their axils are situated the 4-rowed, spike-like male and scarlet-coloured female cones, upon dichotomous branches. The perianth consists in the ♂ of 2 alternating pairs of leaves, the inner ones of which are slightly united. The andrœcium likewise consists of 2 whorls: the external (transverse) with 2, the internal with 4 stamens; the lower halves of the 6 filaments uniting to form a cup. Each of the terminal anthers corresponds to a sorus of 3 sporangia, the sporangia being fused together, and opening at the top by _one_ three-rayed cleft. In the centre of the ♂-flower there is a sterile ovule. In the ♀-flower a perianth of two connate leaves is present.--_Ephedra_ (desert plants, especially in the Mediterranean and W. Asia) at first sight resembles an _Equisetum_; the stems are thin, long-jointed, and the leaves opposite, small, and united into a bidentate sheath; ♂-perianth of two connate leaves (median leaves); 2–8 stamens united into a column. Each anther is formed of 2 sporangia (is bilocular). ♀ mainly, as in _Welwitschia_. The seeds are surrounded by the perianth which finally becomes red and fleshy. There are 30 species.--_Gnetum_ has opposite, lanceolate, pinnately-veined, leathery leaves. They are mostly climbers (Lianas) from Tropical Asia and America. The ♂-flowers have a tubular perianth, (formed from two median leaves) which surrounds a centrally-placed filament, bearing 2 anthers. In the ♀-flower there is a similar perianth, surrounding an ovule provided with 2 integuments. The perianth becomes fleshy and envelops the hard seed. 20 species.

From the circumstance of _Welwitschia_ having ♂ flowers which, besides stamens, possess also a rudiment of an ovule, Celakovsky draws the inference that the earliest Gymnosperms had hermaphrodite flowers which from this structure became differentiated entirely into ♂-and ♀-flowers, with the exception of _Welwitschia_ only, in which this differentiation was only carried out in the ♀-flower. This theory has so far been scarcely proved.

=Fossil Gymnosperms.=

The earliest continental plants which are known belong to the CORDAITACEÆ, a group of plants which existed as early as the Silurian period; they were Gymnosperms, but it has not yet been determined whether they were Cycads or Conifers. The CYCADS, even in the Coal period, were scarce; they attained their fullest development in Jurassic and Cretaceous periods, during which they were rich in species and genera, and extended as far as the Polar regions. In addition to these, Taxaceæ, Abietaceæ, and Taxodiaceæ appeared in the Carboniferous period. The TAXACEÆ appear to have attained their culmination in the Jurassic and Cretaceous periods; _Ginkgo_ appears in the Rhætic; _Torreya_, in the Cretaceous; _Taxus_ and _Podocarpus_ in the Tertiary periods. The ABIETACEÆ also appear in the Carboniferous; _Pinus_ was first known with certainty in the English Weald and in the Cretaceous; almost all other contemporary genera are represented in this latter period. The ARAUCARIACEÆ first appear, with certainty, in the Jurassic. The TAXODIACEÆ may be traced back as far as the Carboniferous (?); _Sequoia_ is first found in the lowest Cretaceous, at that period it spread throughout the entire Arctic zone, and being represented by a large number of species, formed an essential part of the forest vegetation. _Sequoia_ played a similar part in the Tertiary period. The CUPRESSACEÆ are first known with certainty in the Jurassic, but they appeared more frequently and numerously in the Tertiary period, in which most of the present living genera were to be found. The GNETACEÆ, according to a theory advanced by Renault were represented in the Coal period by the genus _Stephanospermum_, which had four ovules enclosed by an envelope.

DIVISION V.

ANGIOSPERMÆ.

See pages 3 and 224. To this Division belong the majority of the Flowering-plants. They are divided into two parallel classes, the Monocotyledons and the Dicotyledons, which differ from each other not only in the number of cotyledons, which, with a few exceptions, is one in the former, two in the latter, but also in the internal structure of the stem, the venation of the leaves, the number of the parts of the flower, etc. ~Assuming that these two classes have sprang from a common origin, it is amongst the Helobieæ in the first, and amongst the Polycarpicæ in the second class that we might expect to find closely allied forms, which might reasonably be supposed to have varied less from this original type. As for the rest, they seem to stand quite parallel, without exhibiting any close relationship. It is scarcely proved that the Monocotyledons are the older class.~

[Our knowledge of the forms included under the Angiosperms has recently been considerably increased by Treub (_Ann. d. Jar. Bot. d. Buitenzorg_, 1891), who has shown that the Casuarinas differ in many important points from the typical Angiosperms. Among other characters the pollen-tube is found to enter the ovule near the chalaza and therefore at the opposite end to the micropyle, and Treub therefore suggests that these plants should be placed in a subdivision termed Chalazogams.

According to this view the principal divisions of the Angiosperms would be represented thus:--

=Angiospermæ.=

Sub-division. Sub-division. CHALAZOGAMES. POROGAMES.

Class. Classes. Chalazogames. Monocotyledones, Dicotyledones.

More recently Nawaschin (_Bull. Acad. Imp. Sci. St. Petersb._, ser. iii., xxxv.) has shown that _Betula_, and Miss Benson (_Trans. Linn. Soc._, 1894) that _Alnus_, _Corylus_, and _Carpinus_ also belong to the Chalazogams.

Our knowledge, however, is still so incomplete that one would hesitate to accord the full systematic value which Dr. Treub attaches to his discovery until the limits of the Chalazogamic group are better defined; and it would hardly be justifiable to include the Casuarinas and the above-noted genera in one family.]

Class 1. =Monocotyledones.=

_The embryo has only one cotyledon; the leaves are as a rule scattered, with parallel venation; the vascular bundles of the stem are closed, there is no increase of thickness. The flower is typically constructed of five 3-merous whorls, placed alternately._

THE EMBRYO is generally small in proportion to the abundant endosperm (exceptions, see _Helobieæ_), and its single cotyledon is often sheath-like, and very large. On the germination of the seed either the entire cotyledon, or its apex only, most generally remains in the seed and absorbs the nutritive-tissue, while the lower portion elongates and pushes out the plumule and radicle, which then proceed with their further growth. The primary root in most cases soon ceases to grow, but at the same time, however, numerous lateral roots break out from the stem, and become as vigorous as the primary root, or even more so. Increase in thickness does not take place in these roots; they branch very little or not at all, and generally die after a longer or shorter time.

THE STEM is frequently a corm, bulb, or other variety of underground stem, as the majority of the Monocotyledons are perennial, herbaceous plants; it has scattered, closed vascular bundles (Fig. 276), and no cambium by which a continuous thickening may take place. The stem of the Palms, however, attains a very considerable thickness, which is due to the meristem of its growing-point continually increasing in diameter for a lengthened period (often for many years), until it has reached a certain size. In this condition the growing-point has the form of an inverted cone, and it is only when this cone has attained its requisite size that the formation of a vertical cylindrical stem commences. Certain tree-like Liliaceæ, as _Dracæna_, _Aloe_, etc., have a continuous increase in thickness; this is due to a meristematic layer, which arises in the cortex, outside the original vascular bundles, which were formed at the growing-point of the stem. This meristem continues to form thick-walled parenchyma and new, scattered vascular bundles. The primary vascular bundles, in the Palms and others, run in a curved line from their entrance into the stem at the base of the leaf, towards the centre of the stem, and then bend outwards and proceed downwards in a direction more parallel to the sides of the stem (Fig. 277). The bundles formed later, in those stems which increase in thickness, are not continued into the leaves.

THE BRANCHING as a rule is very slight, the axillary buds of the majority of the leaves never attaining development, _e.g._ in the Palms, bulbous plants and others. As the cotyledon arises singly, the succeeding leaves also must be scattered, but they are frequently arranged in two rows (Grasses, Iris, etc). _The first leaf borne on a branch_ (the “Fore-leaf,”[24]--the bracteole, if on a floral shoot) has generally, in the Monocotyledons, a characteristic form and position, being situated on the posterior side of its own shoot, and hence turned towards the main axis; it is sometimes provided with two laterally-placed keels (Figs. 279 _f_, 290 _øi_), but the midrib is often absent. It arises in some cases from two primordia, which at the beginning are quite distinct, and thus has been regarded as formed by two leaves. It is, however, only one leaf, a fact which is evident from several circumstances, one being that it never supports more than one shoot, and this stands in the median plane (Fig. 279).

THE LEAVES are _amplexicaul_, and have a large sheath but no stipules; the blade is most frequently long, ligulate, or linear, entire, with parallel venation, the veins being straight or curved (Figs. 300, 309). Connecting the large number of veins which run longitudinally, there are as a rule only weak transverse ones. It is very rarely that other forms of leaves are found, such as cordate (Figs. 302, 312), or that the blade is branched, or the venation is, for example, pinnate or palmate (Figs. 225, 298); these deviations are especially found in the Araceæ, the Palms, the Scitamineæ (Fig. 308), the Dioscoreaceæ, and in several aquatic plants. The incisions in the Palm-leaf are derived by the splitting of an originally entire leaf.

THE STRUCTURE OF THE FLOWER is generally as follows: Pr3 + 3, A3 + 3, G3, rarely S3 + P3 with the other members unchanged.[25] Instead of 3, the numbers 2 and 4 may occur; rarely others. In all these instances there are 5 whorls, which regularly alternate with one another, most frequently in the 3-merous flower, as in the diagram (Fig. 278). This diagram is found in the following orders: Liliaceæ, Convallariaceæ, Juncaceæ, Bromeliaceæ, Amaryllidaceæ, Dioscoreaceæ, Palmæ, some Araceæ, and in some small orders, and may be considered as the typical structure and also the starting point for the exceptional orders. The ovary in many Monocotyledons has many ovules, and the fruit becomes a many-seeded berry or capsule; this form is no doubt the oldest. In others the number of seeds becomes reduced to 1, and the fruit then becomes a cypsela, or a drupe (_e.g. Gramineæ_, _Cyperaceæ_, _Palmæ_, etc).

Deviations from this typical floral structure in some instances may be traced to _suppression_, very rarely to a _splitting_ of certain members, the typical relative positions not being changed. Thus, the Iridaceæ, the Cyperaceæ, most of the Gramineæ and some Juncaceæ deviate in having only 3 stamens (Fig. 279), the inner whorl (indicated by *) not becoming developed. The Musaceæ differ in the posterior stamen not being developed; _Zingiberaceæ_ (Fig. 314), _Marantaceæ_, and _Cannaceæ_, in the fact that only 1 of all the stamens bears an anther, and the others are either suppressed or developed into petaloid staminodes, with some perhaps cleft in addition. The Orchideæ deviate in having, generally, only the anterior stamen of all the 6 developed (Fig. 280). In this, as in other instances, the suppression of certain parts of the flower is often connected with _zygomorphy_ (_i.e._ symmetry in _one_ plane), chiefly in the inner perianth-whorl, but also in the other whorls. In the Orchids, the perianth-leaf (the labellum, Fig. 280 _l_) which is directly opposite the fertile stamen, is larger and altogether different from the others. The perianth-leaves may also be suppressed; see, for example, the two diagrams of the Cyperaceæ (Fig. 284). In some orders the suppression of these leaves, which form the basis of the diagram, is so complete that it is hard to reduce the actual structure of the flower to the theoretical type, _e.g._ the Grasses (Fig. 290) and _Lemna_ (Fig. 303). In the first family, which especially comprises water-plants, a somewhat different structure is found; thus Fig. 282 differs somewhat from the ordinary type, and other flowers much more so; but the floral diagrams which occur in this family may perhaps be considered as the most probable representatives of an older type, from which the ordinary pentacyclic forms have taken their origin. In favour of this theory we have the larger number of whorls, the spiral arrangement of some of these in the flower, with a large and indefinite number of stamens and carpels, the perfectly apocarpous gynœceum which sometimes occurs, etc., etc.

The Monocotyledons are divided into 7 Families:--

1. HELOBIEÆ. This family forms a group complete in itself. It commences with hypogynous, perfect flowers, whose gynœcium is apocarpous and terminates in epigynous and more or less reduced forms.

2. GLUMIFLORÆ. These have as a starting point the same diagram as the following families, but otherwise develope independently.

3. SPADICIFLORÆ. Also an independent branch, or perhaps two different ones which terminate in much reduced forms.

4. ENANTIOBLASTÆ. These ought perhaps to be amalgamated with the following family.

5. LILIIFLORÆ. These advance from forms with the typical diagram and hypogynous flower, to epigynous and reduced forms.

6. SCITAMINEÆ and

7. GYNANDRÆ. Two isolated families, which probably have taken their origin from Liliifloræ, and have epigynous, mostly zygomorphic, and much reduced forms.

Family 1. =Helobieæ.=

To this family belong _only water- or marsh-plants_; _the endosperm is wanting_, and they possess an embryo with a very _large hypocotyl_ prolonged downwards and often club-like. The perianth is often differentiated into calyx and corolla; the flower is regular, and in the first orders to be considered, may be reduced to the ordinary Monocotyledonous type; there are, however, _usually found two_ 3-_merous whorls of carpels_ (Fig. 282), and thus in all 6 whorls, or again, the _number of carpels may be indefinite_; the number of stamens also may be increased, either by the division of the members of a whorl, or by the development of additional whorls. _Syncarps_,[26] with nut or follicular fruitlets, are _very common_, for example, in the first orders; in the last (Hydrocharitaceæ) the carpels are not only united, but the ovary is even inferior.

The primitive type appears to be a hypogynous flower, similar to that of the Juncaginaceæ or Alismaceæ, with several 3-merous whorls, and free carpels, each with many ovules; the green perianth in this instance being no doubt older than the coloured ones. If we take a flower with this structure as the starting point, then the family developes partly into epigynous forms, partly into others which are so strongly reduced and exceptional that it is scarcely possible to refer them to the ordinary type. The family, through the peculiar _Zostereæ_, appears to approach the Araceæ, in which _Potamogetonaceæ_ and _Najadaceæ_ are included by some authorities. However, the inclusion of _Potamogeton_, and with it _Ruppia_ and _Zannichellia_, in the Juncaginaceæ appears quite correct. It would scarcely be right to separate _Zostereæ_ from these. Great stress has often been laid upon the similarity with the Ranunculaceæ which is found in the Alismaceæ, but it is scarcely more than an analogous resemblance.