42 VEGETABLE PHYSIOLOGY. [LESSON 14. 



249. Sometimes they are composed of a single cell, which is sim- 

 ple and undivided, or forked, or branched ; at other times they are 

 composed of many cells, either placed end to end, or united together 

 laterally, and gradually forming a cone, as in compound hairs. 



250. Hairs occur on various parts of plants ; as the stem, leaves, 

 flowers, seed-vessels and seeds, and even in the interior of vessels. 



251. Hairs are developed occasionally to a great extent on plants 

 exposed to elevated temperatures, as well as on those growing on 

 lofty mountains. Different parts of plants are transformed into 

 hairs, as may be seen in the flowering stalks of Ehus Cotinus, and in 

 the calyx of Composites. 



FIG. 73. FIG. 74. 



Macuna pruriens, or Oowitch. Dioncea muscipula, or Venus' Fly-trap. 



252. On the pod of the Cowitch (Macuna pruriens), hairs are 

 produced with projections on their surface, which cause great irrita- 

 tion when applied to the skin (Fig. 73). 



253. In Venus' Fly-trap (Dionwa muscipula), stiff hairs exist on 

 the blades of the leaf (Fig. 74), which, when touched, cause them to 

 close (a), thereby impaling the fly. 



254. Cotton is simply the hair surrounding the seeds of Gossipi- 

 um herbaceum ; as they dry, they collapse into a flat band with 

 rather rounded borders, and ultimately become twisted (Fig. 75) ; by 

 these characters, the fibre of cotton can be readily distinguished un- 

 der the microscope from all other tissues, and when associated with 

 flax, can be identified, and counted with great precision. 



255. The hairs most frequently met with in plants are called 

 lymphatic, from their not being connected with any particular secre- 

 tion. Those, on the other hand, which have secreting cells at their 

 base, or apex, are called glandular hairs. 



