8 BOTANY. 



different names are given to surfaces, according to the degree to which 

 hairs are developed, as well as according to the nature of the hairs them- 

 selves. Thus, a surface is glabrous, when there are no hairs whatever ; 

 pilose or hairy, when such exist; villous, when the hairs are long, weak, 

 and often oblique ; sericeous, when the hairs are long and adpressed, 

 with a silky lustre ; hispid {hirtus), when the hairs are long and stiff, but 

 not adpressed ; hirsute, when they are long, but neither stiff nor adpressed, 

 velvety {velutinus), when there is a dense covering of short down, like 

 velvet ; tomcntose, when the surface is covered with crisp, rather rigid 

 entangled hairs, like cotton, forming a kind of felt ; ivoolly, when the hairs are 

 long and matted, like Avool ; bearded or stupose, when the hair occurs in small 

 tufts. 



As glandular hairs differ in nothing but form from true glands, we shall 

 consider both together. A gland is a cavity in the epidermis, with variously 

 shaped walls, usually inclosing a. peculiar secretion. When supported on 

 a stem, glands are petiolate, stipitate, or stalked; when without this, they 

 become sessile. Stalked glands, or glandular hairs, are composed either of 

 a single cell, dilated at the apex, or of several combined. The gland is 

 sometimes situated at the base of the hair, which is perforated to receive the 

 secretion, as in the common nettle. Here the apex is closed by a solid cap, 

 which breaks off at the slightest touch, leaving the poison to pass into the 

 wound. 



Glands sometimes occur as secreting cells surrounding a ^pit or depression. 

 These communicate with the surface by means of a canal. Sometimes only 

 the apex of the gland comes to the surface, at others it is entirely below ; in 

 this latter case the gland is vesicular. Warts {verruca^) are collections of 

 thickened cells on the surface of plants, containing various matters. Lenticels 

 are cellular projections on the surface of bark, arising from its inner por- 

 tion. 



The sbjcct of the epidermis atid its appendages is to protect the plant from 

 noxious influences, whether atmospheric, meteorological, or animal. Thus, in 

 dry climates it is very thick, and coated with a waxy secretion, to prevent the 

 loss of water. The stomata permit the escape of fluid from the interior, and 

 exhibit a compensating contrivance, by which, when the plant is distended 

 with liquid, they are opened to their utmost, closing more and more with the 

 loss of moisture. A communication is kept up between the air and inner bark 

 by means of lenticels, which thus perform the functions of stomata. The 

 young roots are produced from them under certain circumstances. Some hairs 

 occurring on the stile of flowers are called collecting hairs, from the office they 

 possess in taking up the pollen. In many hairs, especially in those of 

 Tradescantia or spider wort, a circulation of fluids may readily be seen to take 

 place, called Cyclosis. 



2. Descending Stem or Root. 

 The truly compound organs of the plant are the axis and its appendages. 



