Variation in the Food Reserves of Trees. 237 



The conclusions of the foregoing contributions may be sum- 

 marized briefly in the following sentences : 



Starch. — (i) There is common agreement that in the cortex 

 and phloem of young branches reserve starch accumulates from 

 early summer till autumn, then gradually diminishes in amount 

 to a minimum, or to nothing through the winter; then in early 

 spring reappears in large quantity, to diminish to a second mini- 

 mum as the buds are unfolding. 



(2)) In the xylem of young branches and trunks, it is agreed 

 that there is, in winter, a reduction in some trees, in some, a total 

 disappearance of starch. 



(3) In the relatively few statements regarding the presence 

 of starch in roots, there is agreement that there is much less 

 seasonal variation than in stems. Starch remains in both phloem 

 and xylem of the root through the winter, and reaches a minimum 

 there in early summer. 



(4) In the older trunks and older branches of the Norway 

 Spruce, according to Fabricius, there is not so great a seasonal 

 variation as in the younger stems. In the older stems, the starch 

 in both phloem and xylem remains the year through, though with 

 some reduction in late autumn. 



Sugar. — ^According to the extensive work of Fischer, sugar 

 shows a maximum in December, and a lesser maximum in early 

 spring, its maximum coinciding with the minimum of starch. 

 Most authors agree with Fischer, and believe that these sub- 

 stances have a reciprocal action in changing the one into the other. 

 Mer, however, as the result of several analyses, concluded that 

 there is no more sugar present in winter than in summer. Sablon 

 also found only a small increase of sugar in winter. 



Fat. — Although Fischer and one or two other authors believed, 

 on rather insufficient evidence, that starch was transformed into 

 fat in early winter, the most of the writers agree that the amount 

 of fat present has no relation to the transformations of starch. 

 The most that can be said is that fat is at a minimum in early 

 summer, and that it increases from this time till January, and 

 then begins a decline lasting till May or June. 



Cellulose. — Only two authors have written on cellulose as a 

 food reserve — Sablon and Schellenberg. If Sablon's conclusions 

 are correct, then the amount of reserve cellulose is considerably 

 greater than the combined amounts of starch, sugar and fat. 



