LESSON 14.] 



HAIRS. 



43 



256. Glands are collections of cells forming secretions ; they are 

 either stalked or not stalked. The former are glandular hairs, hav- 

 ing the secreting cells at the apex. 



FIG. 75. FIG. 76. 



Fibres of cotton (Gossipium herbaceum). 



Hairs of plants. 



FIG. 78. 



257. These stalked hairs are either composed of a single cell, with 

 a dilatation at the apex (Fig. 76, A), or of several cells united to- 



Fig. 77. gether, the upper one being the secreting organ (Fig. 

 76, B). In place of a single terminating secreting 

 cell, there are occasionally two (Fig. 76, C), or more (D). 



258. Hairs sometimes serve as ducts through which 

 the secretion Of glands is discharged ; these are glandu- 

 lar hairs, with the secreting cells at the base. Such 

 hairs are found in the ommon nettle (Fig. 77), in 

 Loasa, or Chili nettle, and in Malpighia, and are usu- 

 ally called stings. 



259. In the Nettle (Urtica dioi- 

 ca), they consist of a single conical 

 cell, dilated at its base (see Fig.), 

 and closed at first at the apex by a 

 small globular button placed ob- 

 liquely (a). This button breaks off 

 on the slightest touch, when the 



Hah^uS^i snar P extremity of the hair enters 

 oica (nettle), the skin, and pours into the wound 

 the irritating fluid which has been pressed out 

 from the elastic epidermal cells at the base. 



260. When a nettle is grasped with violence, 

 the sting is fractured, and hence no injury is done Hair, Drosera rotundifo- 

 to the skin. 



