406 Dr. F F. Blackman and Mr. A. M. Smith. [Deec. 19, 
Miss Matthaei* had caused the great significance of this factor to be 
generally recognised. Pantanelli is satisfied with stating that his experi- 
ments were all done between 22° C. and 30° C., within which range 
temperature was then believed to be without any determining effect on 
assimilation. In the course of each single experiment, however, the 
temperature of the water is stated to have varied very little. 
In Pantanelli’s experiments the small sprig of Elodea, 1 cm. long, was 
contained in a large cubical glass vessel of CO2-laden water, and this was 
moved along through a series of increasing or decreasing light intensities, 
staying exactly 10 minutes in each position. 
The first point for comment is that the rate of bubbling did not remain 
constant minute after minute in each position, but nearly always fell off 
steadily all the time. This effect is slight in weak hghts but strongly 
marked in intense lights. 
This falling off in time may be partly due to external factorst and partly 
to internal causes which may be aggregated as the “ time factor.” 
An effective cause of decline is to be found in the protoplasmic disturbance 
produced by the intense radiation of hghts 16 to 64 times the intensity of 
direct sunlight. The excess light absorbed by the chlorophyll will cause 
considerable local heating of the plastids, which will depress their activity 
generally, as may also its direct photo chemical action. In accordance with 
this view it is only with these higher intensities of hght that the falling off is 
somarked. Further, the effect is cumulative in Pantanelli’s procedure because 
Elodea is not exposed to light 64/1 without having first stayed ten minutes 
in each of the lights 9/1, 16/1, 25/1, 36/1, and 49/1. Thus the assimilation 
value for each intensity is depressed by the sum of the injurious effects of 
all the previous members of the series, and cannot be brought forward as 
the value of assimilation really corresponding to that intensity of light.f 
With such a series of changing values, there arises at once the question as 
to which value is to be taken as best representing numerically the assimila- 
tion proper to that set of conditions. Pantanelli arbitrarily assumes that 
* Matthaei, “‘ Assim. and Resp., III,” ‘ Phil. Trans.,’ 1904, B. 
+ One may wonder whether the stagnation of the water and slow diffusion of CO, had 
anything to do with these falling values. Prolonged experiments in one vessel of water 
certainly need artificial stirring. In Pantanelli’s apparatus the water could be made to 
flow through the vessel, but it is not clear that it was his practice to have it so. 
F. Darwin and D. M. Pertz have shown how striking is the effect of stirring (“On the 
Effect of Water-currents on the Assimilation of Aquatic Plants,” ‘Camb. Phil. Soc. Proe.,’ 
1895, vol. 9, p. 76). 
t No attempt is made to get information on this matter by determining, for comparison, 
the rate of bubbling when Elodea is exposed straight away to 64/1 without passing 
slowly up the whole series of lights. 
