52 NUT GROWING 



physiology in their bearing upon this part of the sub- 

 ject. The plant takes from the ground only water 

 and mineral salts in solution. These are absorbed 

 chiefly by the young roots and principally by the 

 root hairs of young roots. On that account we need 

 not plant a large unbroken root system when we are 

 transplanting trees. The larger the mass of old roots 

 to be supported the greater the demand that must 

 be made upon the plant for growing a lot of young 

 roots with new root hairs. The green parts of the 

 top of the plant absorb carbon dioxide together with 

 some oxygen and some water vapor; on the other 

 hand they give out carbon dioxide, oxygen, and 

 water vapor. The amount of water vapor given off 

 by a fully developed walnut tree should amount to 

 somewhere between two and three hundred pounds 

 per day according to experiments which have been 

 made with other fruit trees. This relates also to 

 grass and other plants beneath the nut trees. It 

 means that the demand upon soil water is so great 

 that methods for reducing the competition between 

 the nut trees and other plants in the vicinity are in 

 order. In semi-arid regions trees grow so far apart 

 as to represent a parklike aspect. Each tree appar- 

 ently requires water from a range far beyond that 

 of its spread of limbs. Carbon dioxide, which is 

 taken from the air, is employed by the plant for mak- 

 ing chemical combinations with inorganic material 

 taken up by the roots and this is transformed into 

 organic products, carbohydrates and proteins, which 

 are employed for immediate nutrition of the plant in 



