322 HOW PLANTS LIVE AND WORK. 



The finest of these pipes in the leaves are open at the ends, and 

 thus every cell is bathed in "sap." The word " cell " will be referred 

 to later. All these water-bearing pipes (called vessels) originate 

 in the roots. The main root is a downward continuation of the 

 stem. " This " tap-root " branches much in the same way as the 

 stem. The finer branches divide again and again, and the finest 

 branches of all push their way between the particles of soil, seek- 

 ing assiduously for water. These finest branches are, of course, 

 excessively delicate, and they are protected at their tips by minute 

 caps like tiny thimbles. A little way behind these caps the root- 

 lets are covered by closely set hairs, like very fine velvet pile. 

 These root-hairs take in the water which flows up the pipes. Now, 

 the water in soil is never pure ; it contains various salts dissolved 

 in it, and these salts are worked up, mainly in the leaves, into 

 valuable products. 



To return to the roots. It was proved in the summer of 

 1894, by a German botanist, Pfeffer, that there is a very sensitive 

 region just behind the tip of the root. This part acts as the 

 plant's brain, and decides whether it is wise to grow in a certain 

 direction or not. There is something marvellously approaching 

 intelligence in the manner in which a root turns aside from a sharp 

 piece of glass. The absorption of water from the soil is not the 

 only work the root performs. By spreading about in every 

 direction it fixes the plant firmly in the earth. As a matter of 

 fact, absorption takes place only in the very limited regions 

 covered by the fine root-hairs. 



So far, then, we have seen that the whole plant is permeated 

 with a fine network of irrigating canals which convey water from 

 the roots up the stem to the leaves. We have next to see what 

 the leaves are for, and to what use they put the water which 

 reaches them from the roots. We have already noticed that the 

 leaves are shaped somewhat like a lance-head. They are flat, 

 and take a more or less horizontal position. Above all, they are 

 green. Now, if we make an exceedingly thin slice across a leaf 

 by means of a very sharp razor, we shall find on examining the 

 slice with a microscope that the whole of its interior, with the 

 exception of the veins, is made up of myriads of minute bodies 

 called cells. In the upper part of the leaf these cells are arranged 



