346 The Philippine Journal of Science m& 



If there were two limiting factors, then the intensity of both 

 would have to be increased to augment the rate of the process, 

 as increasing only one would still leave the other as a limiting 

 factor. It would follow from this that it could not be possible 

 under any condition to increase the intensity of either of two 

 factors independently and get an increase in the rate of a pro- 

 cess in both cases; for, if either were limiting, an increase in 

 the intensity of the other would be without effect. On the other 

 hand, if neither factor were limiting, then some other would be, 

 and an increase in the intensity of either or both of the two 

 factors that are not limiting would be entirely without effect. 

 This point of view is clearly shown in Blackman's discussion 

 in the paper cited above, and also in a paper on assimilation 

 in submerged water plants. 5 



In the latter paper Blackman and Smith determine the rela- 

 tion of variations in the concentration of carbon dioxide to 

 photosynthesis ; also of two different temperatures and two light 

 intensities to photosynthesis. They presented these results in 

 the form of a diagram on page 402, in which the ordinates 

 represent the assimilation. Separate ' curves were drawn re- 

 presenting the relation to assimilation of the carbon-dioxide 

 supply, the temperature, and the illumination. Concerning these 

 curves they write as follows : 



* We can by inspection tell exactly what minimum of CO=, 

 temperature, and light will be required for any one of the values of 

 assimilation on the ordinates by following the horizontal line right across 

 the diagram and noting where it intersects the three curves respectively. 

 Reciprocally, given any hypothetical combination of different magnitudes 

 of the three factors, we have only to note in the diagram the values of 

 assimilation corresponding to each of them, and we can foretell that the 

 value of assimilation actually attained in that combination will be the 

 lowest of the three values. 



Now, according to this last quotation, if temperature were 

 the limiting factor, an increase in carbon-dioxide supply or illu- 

 mination would appear to have no effect. Blackman and 

 Smith's paper was supposed to demonstrate the action of the 

 theory of limiting factors as proposed by Blackman. 6 It may, 

 therefore, be interesting to examine some of the results. 



The first section of the paper deals with the relation of the 



-r 'Blackman, F. P., and Smith, A. M, Experimental researches on 

 vegetable assimilation and respiration. IX.— On assimilation in submerged 

 water-plants, and its relation to the concentration of carbon dioxide and 

 other factors, Proc. Roy. Soc. London B83 (1910-1911) 389-412 

 6 Blackman, F. F., and Smith, A. M., op cit 



