ON GARDENING 



Of course it is possible to overdo the matter, 

 super-saturating the soil and so shutting off air 

 from the plant roots. But that aspect of the sub- 

 ject will claim our attention in another connection. 

 How THE Plant Uses Water and Air 



If we would have a clear comprehension of the 

 function of water in a plant, we must go a little 

 more fully into the physiology of plant growth, fol- 

 lowing the water, with its salts in solution, from 

 the rootlet by which it is absorbed up through the 

 stem of the plant to the leaf. 



In an earlier chapter something has been said 

 as to the forces that operate to make the water rise 

 in seeming defiance of gravitation from the root 

 to the leaf system of a plant of whatever size. The 

 rise of the watery juices in a garden plant does 

 not seem, perhaps, quite as mysterious as the rise 

 of the sap in a tall tree. But there is no difference 

 in principle. The laws that govern the movement 

 of the sap are quite the same in each case. 



We saw that there is reason to suppose that the 

 principle of osmosis, acting betv/een the cells, has 

 an important share in transferring water from one 

 cell to another, and ultimately, step by step, from 

 the root to the topmost leaf. 



It should be added, however, that the entire 

 subject of the rise of sap in the tree has been mat- 

 ter for debate, and that there is not entire una- 



[17] 



