40 
JOHN H. EHLERS 
— 6° C. to 38° C. the curve is convex to the temperature abscissa, the 
maximal amounts increasing rapidly as the temperature increases. 
For example, the maximal amounts increase from 0.2 mmg. of CO2 
per hour for 50 sq. cm. of leaf surface at — 6° C. to 3.8 mmg. at 9° C. 
The conclusion is that, other conditions being favorable, assimilation 
increases directly with the temperature; that for each temperature 
there is a definite amount of assimilation beyond which a further 
increase in light intensity produces no eflfect except in so far as it 
increases the internal temperature of the leaf. A greater assimilation 
can be obtained only by increasing the temperature. The author 
considers temperature, therefore, as the fundamental condition 
governing assimilation, intensity of light as well as percentage of 
CO2, since they are always present in sufficient quantities, being of 
secondary importance. 
3. Accumulation of Reserve Food Material hy evergreen Trees 
in Winter 
In 1904 Sablon (23) published the results of his investigations 
on the reserve material of deciduous trees. He found that the reserve 
carbohydrates of these trees reached a maximum in autumn at the 
fall of the leaves at the end of the period of active assimilation. Dur- 
ing the winter the reserve decreased a little, while in the spring during 
the formation of new shoots there was a decided diminution — a fall 
to the minimum. Two years later (24) he published the results of an 
investigation of the reserve materials of evergreen trees (les arbres a 
feuilles persistantes). The species used were Quercus Ilex, Pinus 
laricio, Larix europoea, and Evonymus japonicus. The determinations 
in both investigations were made by chemical analysis. The results 
obtained in this investigation were strikingly different from those 
obtained with deciduous trees. Instead of the maximum appearing 
in autumn, there is a constant increase in reserve material during the 
winter, and a maximum is reached only at the beginning of spring. 
To quote directly: ''Pendent I'hiver, en effet, la vegetation est sus- 
pendu, par consequent la depense de reserve est faible; d'autre part 
I'assimilation du carbone se poursuit et Ton sait que I'abaissement de 
la temperature affaiblet beaucoup mains I'assimilation que la respir- 
ation. II est done naturel que I'hiver soit pour les arbres a feuilles 
persistantes une period de formation de reserve." In other words, 
in trees with persistent leaves photosynthesis is not only sufficient 
