52 THE ELEMENTARY STRUCTURE OP PLANTS. 



70. StomatCS {Stojnata) OF Breatlling-Porcs. These have a peculiar 

 structure, the opening being guarded usually by a pair of thin-walled 

 cells, so arranged as to close or open according to circumstances. 

 They will also be illustrated in the chapter on the Leaves, to wliich 

 they more particularly belong. 



71. Ilairs are external prolongations of cells of the epidermis, con- 

 sisting 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. In what are called Glandular Hairs, or 

 Stalked Glands, the upper cell or cluster of cells has a peculiar 

 structure, and elaborates peculiar (usually odorous) products, such 

 as the fragrant volatile oil of the Sweetbrier. 



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

 especially to superficial appendages of the epidermis which elaborate 

 odorous or other products. 



73. Stings, or Stinging Hairs, such as those of the Nettle, gener- 

 ally consist of a rigid and pointed cell, borne on an expanded base, 

 or gland, which secretes an irritating fluid. 



74. Bristles (Setce) are rigid, thick-walled hairs, usually of a single 

 cell. But the name is likewise given to any similar bodies, of what- 

 ever nature. 



75. Prickles are larger and indurated, sharp-pointed processes of the 

 epidermis or the bark (but not of the wood) ; such as those of the 

 Rose and Blackberry. 



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

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

 fixed by its centre to the epidermis. They are well shown in the 

 Oleaster, Shepherdia, and most silvery leaves like theirs. Our 

 species of Vesicaria exhibit beautiful gradations between these and 

 star-shaped (stellate) hairs. 



Sect. IV. Of the Contents of Cells. 



77. These comprise all the products of plants, and also the 

 materials plants take in from which these products are elaborated. 

 To treat of them fully would anticipate the topics which belong to 

 the chapter on Nutrition. Some of the contents of cells, however, 

 have already been mentioned, in the account of their production and 



