36 AGRICULTURE 



a comparatively strong solution of sugars, 

 etc., in the epidermal cells and root hairs, 

 and a very weak solution of mineral matter 

 in the adjacent soil the water carrying 

 the mineral food has the power of passing 

 through the membrane and so of getting 

 inside the plant. Having gained an entrance 

 it moves upwards, owing to the fact that 

 water is constantly being expired from the 

 upper part of the plant; and in some way, 

 not yet altogether satisfactorily explained, 

 the water, with what is dissolved in it, 

 moves upwards to replace that which is with- 

 drawn. During the growing season, there 

 is a constantly ascending stream which has 

 its origin in the soil and its destination in the 

 atmosphere. The mineral matter present 

 in this ascending stream is not expired into 

 the air, but is retained by the plant and 

 utilized for its vital requirements. Experi- 

 ments have shown that for every pound of 

 dry material ^mineral and organic stored 

 up in the plant some hundreds of pounds of 

 water have passed through the plant tissues. 

 The passage of water through a mem- 

 brane, and its diffusion throughout a solu- 

 tion inside, can be demonstrated in various 

 ways.] If, for instance, we take a hollow 

 glass cylinder, 6 inches or so in length, and 



