Physiological Points IQ 
or the ground lowered, or if the roots fail to be supplied with 
sufficient water, the foliage 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 living on one side feeding the foliage 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 1s cut through, a branch on or near that 
side may die or suffer. 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. 
Anything that prevents the descent of food material from 
the leaves, as when by partial or total girdling‘ 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 foliage, 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 
1 Girdling is the cutting through the cambium layer, or taking off a ring 
of bark around a tree. 
