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 Ceratophyllum 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 





Ml M* Oot Ml .010 .011 01* > 



Carbon-dioxide supply. 



< Olt .010 Off 0!* 0!l Ml CM OK .M» C3$ DM .0*0 Mt .0** Mt 0*4 















































































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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 



