34 



EPIDERMAL APPENDAGES — GLANDS. 



plants. On young roots cellular projections occur (fig. 97 h), which 

 may be called radical hairs. Young leaves and buds are frequently 

 thickly covered with protecting hairs. In this instance the hairs grow 

 chiefly along the veins ; and as the leaves increase in size, and the 

 veins are separated, the hairs become scattered and apparently less 

 abundant. On the parts of the flower (as in the Iris), coloured hairs 

 occur which have been called corolUne. 



Glands are collections of cells forming secretions. The term has 

 been vaguely applied to all excrescences occurring on the surfaces of 

 plants. They are either stalked (petiolate, stipitate), or not stalked (sessile). 



Fig. 91. 



Kg. 90. 



The former may be called glandular hairs, having the 

 secreting cells at the apex. Stalked glands, or glan- 

 dular hairs, are either composed of a single cell, with 

 a dilatation at the apex (fig. 90 a), or of several cells 

 united together, the upper one being the secreting 

 cell (fig. 90 b). In place of a single terminating 

 secreting cell, there are occasionally two (fig. 90 c) or more (fig. 90 d). 

 Hairs sometimes serve as ducts through which the secretion of glands 

 is discharged ; these are glandular hairs, with the secreting cells at the 

 base. Such hairs are seen in the nettle (fig. 9 1 ), in Loasa or Chili nettle, 

 and in Malpighia (fig. 89), and are commonly called stings. In the nettle 

 they are formed of a single conical cell, dilated at its base (fig. 91 6), 

 and closed at first at the apex, by a small globular button placed 



Fig. 90. Glandular hairs, e, Epidennis. a. Hair formed by a single cell, from Sisym- 

 brium chilense. &, Hairs formed of several cells terminated by a secreting cell, from 

 flower-stalk of Antirrhinum majua. ci, Hair composed of several cells, terminated by two 

 secreting cells united laterally, from flower-stalk of Lysimachia vulgaris, d. Compound 

 hair, terminated by several secreting cells united end to end, from Geum nrbanum. Fig. 

 91. Conical hair of tirtica dioica, oi common nettle, ending in a.button or swelling, s, with 

 a dilatation or bulb at its base, 6, which is surrounded by epidermal cells, u e. In this hair 

 there are currents of granular protoplasm, ff. 



