216 BOTANICAL GAZETTE [MARCH 
exposed to diffuse daylight alone the amount of photosynthesis is a measure of the 
light, and it varies with varying light only when the amount of carbon dioxid 
in the atmosphere is artificially increased and the temperature is kept high. Ifnot, 
photosynthesis is limited i and is constant though the light vary. Isolated 
leaves may rise more than 10° C. above a bright mercury thermometer in the 
sun, a result quite at variance with Brown and EscomBr’s results,7 which, how- 
ever, were calculated, not observed. Further study of this point is needed. 
At normal temperature leaves are not able to utilize the full amount of energy 
absorbed; helianthus could reach its maximum at 29° C. with about 68 per cent. 
full sunlight and cherry laurel with about 36 per cent. When light is the limit- 
ing factor equal intensities produce equal photosynthesis with leaves of most 
various structure and type. At low temperatures leaves as different as helianthus 
and cherry laurel have similar photosynthetic maxima, but at high temperatures 
these diverge. Thus at 29.5°C. the former can fix twice as much CO, as the 
latter, requiring twice as much energy to do it, of course. The essential differ- 
ence in the photosynthetic activity in different leaves lies, then, in that they have 
different coefficients of acceleration of this function with increasing temperature. 
So in nature it appears that the low pressure of CO, (entailing slow diffusion 
after solution at the surfaces of the leaf cells) and the low temperatures are the 
serious impediments to food making.— 
Root tubercle cultures——Much interest has been excited during very recent 
years by work done in the Department of Agriculture concerning soil inoculation 
with various root tubercle bacteria. Widespread and rather unfortunate notori- 
t 
knowledge concerning the root tubercle is to be attributed to the recent investi- 
gations conducted i in the Department. This popular impression is of course 
erroneous. The two distinctive contributions to this subject claimed by the 
workers in the Department of Agriculture were that the nitrogen-gathering 
ability of the bacteria was heightened by new cultural methods, and that a 
method of transportation in dried condition, upon cotton, had been devised, 
whereby pure cultures could be distributed readily to farmers. 
Much skepticism has existed concerning the possibility of practically height- 
ening the nitrogen-gathering power of the bacteria, and in a recent bulletin ® 
Harptnc and Prucwa claim to have demonstrated by an examination of 
eighteen of these cotton cultures that such packages are worthless for practical 
— since the organisms are unable to survive upon the cotton or survive 
uch small numbers as to be practically valueless. ‘Substantially identical 
sl upon six of these packages were obtained in five separate laboratories,” 
and the reviewer may add that similar results were obtained in his own 
7 See Bor. GAZETTE 40 : 473. 1905. 
8 Harpine, H. A., and Prucua, N. J., The apa of commercial cultures for 
legumes. N. Y. Agr. Exp. Sta. Bull. 270: 345-385. I 
