EPIDERMAL SYSTEM. 55 



dots in the leaves of the Orange and Myrtle, are compact little 

 clusters of cells filled with essential oil. 



68. Epidermal System, In most plants, except of the lowest 

 grades, {he superficial layer or layers of cells are different from 

 those they envelope. Also certain appendages grow from the 

 surface, which may be briefly noticed here. 



69. The Epidermis, or skin of the plant, is formed of one or more 

 layers of empty cells, with thick walls, cohering so as to form a 

 firm and close membrane, which may be torn off from the subja- 

 cent tissue. It covers all parts of the plant that are directly ex- 

 posed to the air, except the stigrna. Its structure and office will 

 be more particularly described, (and the nature of what has been 

 specially termed the Cuticle explained,) in the chapter on the 

 leaves. 



70. Stomates (Stomata),or Breathing-pores, are orifices connect- 

 ed with a peculiar structure in the epidermis of leaves and other 

 green parts : their structure and office will likewise be described 

 in the chapter on the leaves, to which organ they more particu- 

 larly belong. 



71. Hairs are exterior prolongations of cells of the epidermis, 

 consisting either of single elongated cells, or of several cells placed 

 end to end, or of various combinations of such cells. They are 

 simple or branched, single or clustered (stellate, &c.), and exhibit 

 the greatest variety of forms. They are called Glandular Hairs 

 when the upper cell or cluster of cells elaborates peculiar (usually 

 odorous) products, such as the fragrant volatile oil of the Sweet 

 Brier. 



72. Glands. This name is applied to any secreting apparatus, 

 like glandular hairs, only not raised on a stalk ; and also to other 

 superficial appendages of diverse kinds. 



73. Bristles (Seta) are rigid, thick-walled hairs, usually of a sin- 

 gle cell. But the name is likewise given to any setiform body, of 

 whatever nature. 



74. Prickles are larger and indurated sharp-pointed processes of 

 the epidermis ; such as those. of the Rose and Blackberry. 



75. StillgS, or Stinging Hairs, such as those of the Nettle, gener- 

 ally consist of a rigid and pointed cell, terminating in an expanded, 

 globular base, which secretes an irritating fluid. 



76. Scurf, or Lepidote, Scale-like Hairs, are flattened, star-like 

 clusters of cells, united more or less into a flat scale, which is fixed 



