Physiological Points 19 



or the ground lowered, or if the roots fail to be supplied with 

 sufficient water, the foHage and with it the whole crown will 

 suffer in proportion. 



Generally speaking, each side of the crown is in more or 

 less direct relation with the same side of the root system, the 

 roots Hving on one side feeding the fohage on that side, and 

 vice versa. There is, in other words, more or less direct 

 reciprocity between branch and roots. Hence, if a root on 

 one side of a tree is cut through, a branch on or near that 

 side may die or suft'er. As the shoots lengthen each year, so 

 the roots lengthen; and since only the youngest root tips 

 remain active in taking up water, it stands to reason that 

 they must be fed in order to renew themselves, and to per- 

 form their function. 



Anvthing that prevents the descent of food material from 

 the leaves, as when by partial or total girdhng ' of the tree 

 the conducting tissue is reduced, will therefore starve and 

 eventually kill the root system, partially or entirely. Con- 

 versely, if the root cannot furnish enough water to the leaves, 

 these must wither and die, and finally the whole tree will suc- 

 cumb. Again, if any of the needed minerals are deficient in 

 the soil, this fact will be indicated by at least some abnormal 

 development in the foHage, changes of color, size, form, etc. 

 The interdependence, then, of roots and leaves is complete, 

 an important fact in diagnosing abnormal conditions of 

 either. 



Normally, the leaves elaborate the food' materials during 

 the summer in sufficient quantity to supply all the material 

 of the present year's growth, and, in addition, also accumu- 

 late a surplus, which wanders out of the leaves before their 

 fall, and is stored in the wood to be used for next spring's 



' Girdling is the cutting through the cambium layer, or taking off a ring 

 of bark around a tree. 



