THE EPIDERMAL SYSTEM. 



95 



128.— Triohomes. Under this term are to be included the 

 outgrowths which arise from the epidermis ; they may have 

 the form of hairs, scales, glands, bristles, prickles, etc., and 

 may be composed of single cells, or of masses of cells. 



They originate mostly from the growth of single epidermal 

 cells,* and on their first appearance consist of slightly en- 



FlQ. 81. 



Fie. 80. 



Fig. 80. — TransverBe Bection of epidermis and underlying tissue of ovary of On- 

 eimmta. a, hair of a row of cells ; ft and d, glandular liairs of different ages ; «,/, 

 c, liairs in the youngest stages'of their development. X 100.— After Prantl. 



Fig. 81. — A seedling mustard plant with its single root clothed with root-hairs ; 

 the newest (lowermost) portioil of the root is not yet provided with root-hairs. 



larged and protruding cells (Fig. 80, e, f, c). These may 

 elongate and form single-celled hairs, which may be simple 

 or variously branched. The most important of these hairs 

 are those which clothe so abundantly the young roots of most 

 of the higher plants, end to which the name of Eoot-hairs 



* It is probable that the common statement that trichomes always 

 develop from single cells must be modified. 



