Grosseribacher—Radial Growth in Trees. 
17 
From these j observations on reserve food distribution in large 
trees it seems evident that most of the starch is converted to fat 
during spring and early summer, and reconverted to starch 
again beginning in late September, so that the smaller portion 
of reserve food passes the 'winter as fat. Fischer’s 29 observa¬ 
tions do not agree with those of Fabricius but, since the former 
based practically all his conclusions on specimens from stems 
ten years old or less his conclusions are not surprising. 
According to Fabricius there is a general increase of starch 
also in spring but it is of short duration. By April 22 it had 
largely disappeared from both 'sides of the cambial region and 
more especially toward the top of the tree, i. e., apparently in 
proportion to cambial activity. At the same time the process 
of converting the reserve starch in the older rings to fat (which 
continues all summer) is 1 also going on. The redeposition of re¬ 
serve food is begun in the bark in the form of starch. In the 
wood this process does not'begin till about the last of September 
and not until October is the fat in the wood converted into 
starch. The fat in the bark'is used up during summer and, from 
the peripheral shoots downward, followed by a redeposition of 
starch as the second growth is finished in late summer. Elonga¬ 
tion growth of roots is said to occur chiefly in June and July' and 
again to a slight extent in October. During those periods they 
contained considerable fat which afterwards disappeared. 
This series of examinations has shown 'that the fat content of 
roots is practically proportional to the amount of elongation 
growth in progress and that when this growth ceases very little 
or no fat is present, i. e., a causal relation seems to exist between 
fat content and elongation growth. It is thought that perhaps 
the growing tip secrets an enzyme which is carried up the root 
by the “transpiration current,” and which converts starch to 
fats. After the cessation of growth the fats are again changed 
to starch. 
A more recent contribution to this discussion is by Preston 
and Phillips, 30 but it also is based chiefly on determinations made 
on young trees. The study covered the period from October to 
29 Fischer, A. Beitrage zur Physiologie der Holzgewachse. Jahrb. 
Wiss. Bot 22:73-160. 1891. 
80 Preston, J. F., and Phillips, F. J. Seasonal variation in the food 
reserve of trees. Forest Quarterly 9:232-43. 1911. 
2—S. A. 
