Water-Content of Plants 



47 



they come into the most intimate contact with the minute 

 soil particles, so intimate, at times, that fine particles 

 actually stick into the walls (Fig. 11). They are, there- 

 fore, peculiarly fitted for the needs of absorption, as will 

 be later developed. 



It will also be noted that those regions of the rootlet 

 clothed with root-hairs have ceased to elongate ; that is, 

 so soon as the hairs are developed it is an indication that 

 this portion of the root is fixed in the soil ; otherwise its 

 growth would crush such organs and 

 prevent their further efficiency. In 

 this connection it may, therefore, be 

 observed that the " push " which is 

 needed to force the root forward in the 

 soil is concerned with a relatively short 

 axis, perhaps not more than a quarter 

 of an inch in length. The practical ad- 

 vantages of this mode of growth are 

 obvious upon a moment's reflection. 

 If, for instance, one should attempt to 

 force into the soil a fine wire two feet 

 long, pushing from the upper end, it 

 would certainly bend. In fact, the 

 difficulties of such a mode of growth 

 in the soil practically precludes the pos- 

 sibility of its occurrence. 



The root-hairs are relatively short- 

 lived upon the majority of plants. 

 Their activity may be embraced in a FIG. 11. Root-hairs 

 period of from a few days to a month (a) ? rown in coa ^ 



,.. . . . sand; cortex (0) 



or two, and they are readily injured by and epidermis (c). 



