Grossenbacher Radial Growth in Trees. 17 



From these ; 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 '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 1 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 



19 Fischer, A. Beitrage zur Physiologie der Holzgewachse. Jahrb. 

 Wiss. Bot. 22:73-160. 1891. 



89 Preston, J. F., and Phillips, F. J. Seasonal variation in the food 

 reserve of trees. Forest Quarterly 9:232-43. 1911. 



2 S. A. 



