§ 15. Accessory Organs.

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168. Under this name are included, in many elementary works, various external parts of plants which do not appear to act any essential part either in the vegetation or reproduction of the plant. They may be classed until four heads : Tendrils and Hooks, Thorns and Prickles, Hairs and Glands.

169. Tendrils (cirrhi) are usually abortive petioles, or abortive peduncles, or sometimes abortive ends of branches. They are simple or more or less branched, flexible, and coil more or less firmly round any objects within their reach, in order to support the plant to which they belong. Hooks are similar holdfasts, but of a firmer consistence, not branched, and less coiled.

170. Thorns and Prickles have been fancifully called the weapons of plants. A Thorn or Spine is the strongly pointed extremity of a branch, or abortive petiole, or abortive peduncle. A Prickle is a sharply pointed excrescence from the epidermis and is usually produced on a branch, on the petiole or veins of a leaf, or on a peduncle, or even on the calyx or corolla. When the teeth of a leaf of the stipules are pungent, they are also called prickles, not thorns. A plant is spinous if it has thorns, aculeate if it has prickles.

171. Hairs, in the general sense, or the indumentum (or clothing) of a plant include all those productions of the epidermis which have, by a more or less appropriate comparison, been turned bristles, hairs, down, cotton or wool.

172. Hairs are often branched. They are said to be attached by the centre, if parted from the base and the forks spread along the surface in opposite direction; plumose, if the branches are arranged along a common axis, as in a feather; stellate, if several branches radiate horizontally. These stellate hairs have sometimes their rays connected together at the base, forming little flat circular disks attached by the centre, and are then called scales, and the surface is said to be scaly or lepidote.

173. The Epidermis, or outer skin, of an organ, as to its surface and indumentum, is

smooth, when without any protuberance whatever.

glabrous, when without hairs of any kind.

glabrescent, glabrate, becoming glabrous.

striate, when marked by parallel longitudinal lines, either slightly raised or merely dicoloured.

furrowed (sulcate) or ribbed (costate) when the parallel lines are more distinctly raised.

rugose, when rinkled or marked with irregular raised or depressed lines.

umbiiiicate, when marked with a small round depression.

umbonate, when bearing a small boss like that of a shield.

viscous, viscid, or glutinous, when covered with a sticky or clammy exudation.

scabrous, when rough to the touch.

tuberculate or warted, when covered with small, obtuse, wart-like protuberances.

muricate, when the protuberances are more raised and pointed but yet short and hard.

echinate, when the protuberances are longer and sharper, almost prickly.

setose or bristly, when bearing very stiff erect straight hairs.

glandular-setose, when the setæ or bristles terminate in a minute resinous head or drop. In some works, especially in the case of Roses and Rubus, the meaning of setæ has been restricted to such as are glandular.

glochidiate, when the setæ are hooked at the top.

pilose, when the surface is thinly sprinkled with rather long simple hairs.

hispid, when more thickly covered with rather stiff hairs.

hirsute, when the hairs are dense and not so stiff.

downy or pubescent, when the hairs are short and stiff, and lie close along the surface all in the same direction; puberulent, when slightly pubescent.

strigose, when all the hairs are rather short and stiff, and lie close along the surface all in the same direction; strigillose when slightly strigose.

tomentose or cottony, when the hairs are very short and soft, rather dense and more or less intricate, and usually white or whitish.

woolly (lanate), when the hairs are long and loosely intricate, like wool. The wool or tomentum is said to be floccose when closely intricate and readily detached, like fleece.

mealy (farinose), when the hairs are excessively short, intricate and white, and come off readily, having the appearance of meal or dust.

canescent or hoary, when the hairs are so short as not readily be distinguished by the naked eye, and yet give a general whitish hue to the epidermis.

glaucous, when of a pale bluish-green, often covered with a fine bloom.

glaucescent, subglaucous or becoming glaucous.

174. The meanings here attached to the above terms are such as appear to have been most generally adopted, but there is much vagueness in the use practically made of many of them by different botanists. This is especially the case with the terms pilose, hispid, hirsute, pubescent, and tomentose.

175. The name of Glands is given to several different productions, and principally to the four following :-

1. Small wart-like or shield-like bodies, either sessile or sometimes stalked, or a fungous or somewhat fleshy consistence, occasionally secreting a small quantity of oily or resinous matter, but more frequently dry. They are generally few in number, often definite in their position and form, and occur chiefly on the petiole or principal veins of leaves, on the branches of inflorescences, or on the stalks or principal veins of bracts, sepals or petals.

2. Minute raised dots, usually black, red, or dark-coloured, or a resinous or oily nature, always superficial, and apparently exudations from the epidermis. They are often numerous on leaves, bracts, sepals, and green branches, and occur even on petals and stamens, more rarely on pistils. When raised upon slender stalks they are called pedicellate or (stipitate) glands, or glandular hairs, according to the thickness of the stalk.

3. Small, globular, oblong or even linear vesicles, filled with oil, imbedded in the substance itself of leaves, bracts, floral organs or fruits. They are often numerous, like transparent dots, sometimes few and determinate in form and position. In the pericarp of Umbelliferæ they are remarkably regular and conspicuous, and take the name vittæ.

4. Lobes of the disk (137), or other small fleshy excrescences within the flower, whether from the receptacle, calyx, corolla, stamens, or pistil.

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