CONTENTS. Introductory Chapter.-General Principles of Classification.— PAGE. 296 CLASS I. EXOGENS. Sub-Class I. THALAMIFLORE. Order Ranunculaceæ, or Crow-foot Tribe,-Anemony, Hellebore, 346 350 354 358 360 364 368 Nymphaceæ, or Water-Lily Tribe, Victoria regalis, &c. Papaveraceæ, or Poppy Tribe,-Celandine, &c.-Opium Caryophylleæ, or Chick-weed Tribe, Pink, Carnation, Aurantiaceæ, or Orange Tribe,-Lemon, Shaddock, &c. Order Celastrineæ, or Holly Tribe,-Brazilian Tea, Spindle-tree 398 Rhamneæ, or Buckthorn Tribe,-Jujube, Lotus Onagrariaceæ, or Evening-Primrose Tribe,-Willow-Herb, Myrtaceæ, or Myrtle Tribe,-Clove, Pomegranate, &c Passifloreæ, or Passion-flower Tribe,-Grenadilla, &c. Crassulaceæ, or Houseleek Tribe,―Sedum, &c. Saxifrageæ, or Saxifrage Tribe, London Pride, Hydran- Rubiaceæ, or Madder Tribe,-Coffee, Peruvian Bark, &c.. 433 Compositæ, or Composite Plants, Daisy, Sun-flower, Asters, Labiatæ, or Labiate Plants,-Mint, Sage, Rosemary, &c. 457 Solaneæ, or Nightshade Tribe,-Henbane, Tobacco, Po- Order Chenopodeæ, or Goosefoot Tribe,-Spinage, Beet, Rhubarb, Laurincæ, or Laurel Tribe,-Cinnamon, Nutmeg, &c. 532 STRUCTURE OF SEED OF GRAMINEÆ. flower stalk, as is shown in the Rice; this also is termed a glume. Of all these parts, the interior scales are the only ones which bear any resemblance to the calyx or corolla of more perfect flowers; the remainder are to be considered as bracts. B 735. If the ovary be cut across, nothing but a kind of pulp will be found within it; this substance then fills the young ovule, which entirely occupies the cavity of the ovarium; and its own envelopes and the walls of the ovarium grow together, in such a manner as to be scarcely distinguishable. When ripened, however, the ovary becomes hard; and its own walls and the membranes of the seed having coalesced still more closely, all trace of the originally distinct seed vessel is lost. Such a seed, which appears destitute of an external casing, but which has really been developed within one, is properly termed a grain (See § 504). The great mass of the seed consists of the separate albumen; and the embryo itself is very minute, and not easily discovered by an unpractised Botanist. If the grain be laid upon its flat face, so that the convex side is uppermost, a minute oval depression will be seen towards the narrowest end; and if the seed-coat be carefully removed, a little oval body will be found lying half imbedded in the albumen. If this be divided perpendicularly with a sharp knife, it will be found to consist of a thickish scale, which is the single cotyledon; and upon this lies a little conical body, composed of several minute sheaths fitted one over the other, which is the plumula; whilst at the opposite extremity will be found the radicle, or rudiment of the root. When the radicle first begins to grow, the cotyledon swells a little, and attaches itself firmly, by the whole of its absorbent surface, to the albumen; and this, as it is gradually changed in the process of germination, is absorbed by that surface, and supplied by it to the plumula and radicle, until they have attained Fig. 118. Seed of Grass; A, external view, showing a, depression at the end, and b, position of embryo; B, section, showing the plumula a, the radicle b, and the cotyledon c, the whole embryo being on the outside of the albumen d. sufficient development to absorb and prepare nutriment for themselves, by which time the store laid up in the albumen is exhausted. This provision enables the germination of the seed to take place with much greater rapidity than we usually find in those which have a separate albumen; for in the latter, the surface by which the young plant absorbs from it is much smaller, the cotyledon being sent upwards around the young stem. 736. In general, the true stems of Grasses are hidden, like those of several other Endogenous tribes, as well as of Ferns, beneath the earth; and the stalks which bear the organs of fructification are not to be considered in this light. In the Bamboos of tropical climates, however, the true stems elevate themselves into the air, sometimes to the height of 50 or 60 or even 100 feet, sending out lateral branches. The internal structure of the rhizoma of the Grasses is strictly Endogenous; as is that of the culms or hollow stems, if examined at the period of their first development; and their subsequent hollowness results merely from the development of the fibrous portion of their structure, which forms the exterior, faster than the cellular parenchyma increases to fill it. This form of the stem is a very beautiful illustration of the mode in which the greatest possible strength may be obtained with the least expenditure of material. Some of the Grasses have, instead of a rhizoma or an upright stem, a long creeping stem, which runs near or upon the surface, sending down roots into the soil, and developing leaf and flower-buds at intervals. This tendency has already been adverted to as very troublesome in the Couch-grass (Triticum repens); but is of great service to man in a grass termed the Sand-Reed (Arundo arenaria) and others, which can vegetate amidst dry and drifting sand, and are hence employed to give firmness to embankments, which they pierce with an entangled web of living structure, that offers a resistance rarely overcome by the force of storms, and is renewed as fast as it is destroyed. Such grasses do not increase so much by seeds as by the multiplication of buds; and hence they are commonly spoken of as viviparous; cattle will no. eat them, and hence they are providentially adapted to escape that mode of destruction; |