Pot 0: | On Vegetable Assimilation and Respiration. 409 
rate, and here again the zero of bubbling would be at an infinite distance. 
Such methods of presenting facts are obscurantic rather than graphic, and 
we have been compelled to construct the larger outer curve of fig. 8 to 
give the corrected relation of the initial assimilation-values in the different 
intensities of light. 
Inspection of this curve at once shows that we are dealing with a limiting 
factor relation such as we have found in our own work. From intensity 
1/36 to 1/4 the assimilation increases in direct proportion with the increase 
of light and then a limit is reached. Possibly the limit is set by the 
CO.-supply, which did not exceed 15 vols. COz per 100 c.c. of water (0°03 grm. 
COz per cent.). On the other hand, it may have been due to the temperature, 
but we cannot go into this matter as there is no clue to the temperature 
at which this particular batch of experiments was carried out. 
In spite of this uncertainty, it is impossible not to conclude from the 
form of the curve that a limiting factor is at work. Consequently, no 
higher assimilation is ever reached, though the lhght is increased twenty- 
seven fold, up to 9/1. 
_ Pantanelli’s curve of the relation of bubbling-rate to light-intensity 1s 
therefore only really a curve of this nature as regards its first ascending 
part—1/36 to 1/3 light. The next part, 1/3 to 9/1, has nothing to do 
with light, but represents the assimilation corresponding to the limited 
COs-supply or temperature. Finally, we regard the third falling part 
(lights 16/1 to 64/1, shown only in the inset diagram to fig. 8) as nota 
specific assimilation effect at all, but as exhibiting the cumulative effect. 
of depression of protoplasmic activity. 
| As a corollary to his investigation of the light-optimum, Pantanelli 
also made experiments on assimilation, with constant illumination and 
varying CQOb.-supply, to obtain information upon the location of the 
CQO,:-optimum. 
This, he says, he found much less easy to investigate, as simple bubble- 
counting is not satisfactory in strong CO>-solutions. He therefore only 
gives details of three single serial experiments in which, starting with a 
constant light-position, say 1/4 sunlight, the bubbling rate of a shoot of 
Elodea was observed in a succession of cylinders of water with different. 
amounts of dissolved COs, the plant staying 10 minutes in each medium. 
Pantanelli gives (p. 194) the initial and the final timings for the 
liberation of 10 bubbles, during the 10 minutes stay in each concentration 
of COs, for the most satisfactory of his experiments, but there is no curve. 
We have constructed one (fig. 9) from his data, selecting, in each strength 
VOL. LXXXIII.—B. 2H 
