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. n. Root-hairs 

 period of from a few days to a month (a > J rown co 



sand ; cortex (o) 



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



