THE BOOT 19 



Yes, by far the greater part of a tree's food is got by 

 the leaves ; but the tree needs Hme, iron, and other 

 foods that can only be got from the earth.* The tree 

 needs only a very small amount of this root-food, but 

 cannot live without it. If you tear off a fresh green 

 leaf from a plant and put it in water, it will go on 

 making food out of the air, but it has soon to stop ; 

 and one reason is that it can no longer get any root- 

 food ; and, without this root-food, it cannot use the 

 air-food. 



The roots are not made for taking in solid food : 

 they can take in fluids only ; and, therefore, the food 

 must be in a liquid form. This is one reason why 

 the roots must have water. Another reason is that 

 all the materials needed by the tree in its many parts. 

 are water-borne. And, so, without water, food-supplies 

 are soon cut off. 



4. But now you exclaim : " How can water cHmb 

 up a great tree ? " Yes, it is a wonderful piece of 

 work. You will feel this if you carry a bucket of 

 water up a long stair, and remember that a tree can 

 quickly pull up many times this weight. Even a 

 single sunflower can soon pull up a pailful of water. 



5. How can water climb up a tree ? Well, you 

 must know that the root, like every other part of the 

 plant, is built up of tiny cells (See Fig. 13). The 

 root-hairs, too, are just long cells by which the root, 

 drinks. These hair-cells have very thin walls, so 

 that the water gets easily through into the cell. But,, 

 when the water has got inside the cell, it cannot get 

 out again ; and when the cell gets' so full that it can 

 hold no more, it squeezes some water into the next 



* And nitrogea, phosphorus, potash, sulphur, &c. 



