GLANDULAR HAIRS 



105 



of the nature of ethereal oils (cf. p. 62). Such glandular hairs 

 are multicellular and generally consist of a basal cell, which is 

 usually sunk in the epidermis, a projecting stalk, and a glandular 

 head (cf. Fig. 71, g.h.), but are otherwise of very diverse form. 

 In the case of the Chinese Primrose (Primula sinensis, Fig. 50, 

 A-C) and the Garden Geranium (Pelargonium), the head is 

 formed by a single cell and the stalk by a varying number of 

 cells. In the Labiatae (e.g. White Deadnettle) the head is com- 



FIG. 50. Glandular hairs of Chinese Primrose (Primula sinensis, A-C) 

 and Stinging Hair of Nettle (Urtica, D, E). In A-C the secretion 

 is shaded, and in C and E only the greatly magnified tip of the hair 

 is shown. 



posed of four or more cells disposed in a plane parallel to the 

 surface of the leaf. Extended division of the head leads to the 

 peltate type of glandular hair, such as is seen in the Hop (Fig. 

 48, E) and the Black Currant. 



All the cells of such glandular hairs are living, those of the 

 head which are concerned in active secretion being specially 

 characterised by dense protoplasmic contents and large nuclei. 

 Small droplets of secretion can often be recognised within the 

 young glandular cells, but in the mature condition the ethereal 

 oil is found deposited between the cuticle and the cellulose-layer 



