48 NUTRITION. 



water can dissolve; and it is the deposition of 

 this in the stem which gives to all the grasses so 

 much firmness. On the other hand, the pea will 

 reject this, and will take up whatever calcareous 

 substances (or those formed of lime and its com- 

 pounds) the water of the soil contains, these 

 being rejected by the wheat." (Carpenter's Veg. 

 Physiol. p. 89.) On this subject Professor Dau- 

 beny has made many curious experiments. 



38. Plants, then, absorb water by their roots ; 

 but is it pure water only they require ? Modern 

 chemistry has decided this question in the nega- 

 tive. Water in its absolute purity, such as we 

 obtain it by distillation, does not exist in nature : 

 if exposed to the influence of the atmosphere it, 

 holds some of it in solution ; if it is in contact 

 with the soil it will imbibe saline, or organic 

 particles, and thus the water which reaches plants 

 is always more or less charged with other sub- 

 stances. 



39. When water, accompanied by the soluble 

 matter it contains, has entered the spongioles, it 

 becomes a part of the juices of the living plant, 

 is propelled forward with great force, and re- 

 ceives the name of sap. This sap rises in the 

 plant, and probably in its course furnishes the 

 air with which the vessels are filled. The rapidity 



