XIII, C, 6 
Brown: Theory of Limiting Factors 
347 
carbon-dioxide supply to assimilation. The largest number of 
experiments were performed with Elodea and the next largest 
with a bryophyte, Fontinalis. There were also three experi- 
ments with Ceratoyhyllum and one with Potamogeton. 
In these experiments light was measured in arbitrary units. 
The experiments with Elodea were conducted with varying 
amounts of carbon dioxide, varying temperatures, and light 
intensity of either 5.7 or 8.1 units. In plotting the curve for 
Elodea, Blackman and Smith do not indicate either the tem- 
perature or the light intensity for any of these experiments. 
For this reason the results are plotted in fig. 1 of the present 
paper. In this figure the ordinates represent assimilation and 
Carbon-dioxide supply. 
Fig. 1 . Relation of assimilation to supply of carbon-dioxide. Data from Blackman and 
Smith. 
the abscissae the supply of carbon dioxide in terms of grams 
of carbon dioxide in 100 cc of water. The experiments per- 
formed with 8.1 units of light are represented by crosses, and 
those with 5.7 units by continuous circles. The temperature 
at which these experiments were performed is written by the 
point representing the result. The position of Blackman and 
Smith’s curve, as nearly as could be determined, is represented 
by a line of long dashes. According to Blackman and Smith, 
this curve for photosynthesis rises with increasing concentra- 
tions until it reaches a certain point, after which there is no 
further rise, as some other factor (which in this case seems to 
be light) has become limiting. This interpretation is illustrated 
