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its way to the first hair and epidermal cells. Here in 

 case the water supply from the roots were not sufficient, 

 the endosmotic force of these living cells might be able 

 to draw the water through their walls which are them- 

 selves thin, and protected in all cases only by a very 

 thin cuticle. The thin-walled cells of the hair would 

 serve to increase the surface which has the ability to 

 absorb water. 



Supposing this to be one function of the hair, it is 

 plain that the greater the number and size of the thin- 

 walled cells, the greater the ability of the hair to take 

 up water, other things being equal. 



In all the remaining examples of the first class this 

 surface is increased by a greater number of thin-walled 

 cells at the base of the hairs, which always have a 

 greater diameter than that of the upper long cell forming 

 the filz. In some instances this end cell remains small 

 from the beginning, in others it grows to the size of the 

 other cells but losing its contents, collapses so that it 

 is several times smaller than the fresh living cells below. 



In order to verify this hypothesis concerning the 

 hair function, it must first be proved that the surface 

 of the hair is free from any substance which is not easily 

 miscible with water, such as oil, wax, and so forth. 

 At least, it must be shown that if such substances are 

 present they do not act in such a manner as to prevent 

 the action of capillary force. In some instances the first 

 assumption was shown to be true by simply immersing 

 the leaf in water and quickly withdrawing it: while in 

 the water no silvery coating was seen, and when taken 

 out the hairy surface was seen to be completely wet. 

 Quite a large number of leaves, however, when dipped 



