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THE AMERICAN NATURALIST [Vol. XLII 



Let us briefly consider these data. On the katabolic 

 side of metabolism we have the respiratory production 

 of C0 2 , and opposed to it on the anabolic side the intake 

 of carbon in assimilation. 



As a measure of the rate of the metabolic processes 

 constituting growth we have data upon the division of 

 flagellates ; and finally there is the obscure process of cir- 

 culation of protoplasm. 



The intensity of C0 2 production is often held to be a 

 measure of the general intensity of metabolism, but any 

 relation between growth-rate and respiration has yet to 

 be clearly established. Our science is not yet in the stage 

 when quantitative work in relation to conditions is at all 

 abundant; we are but just emerging from the stage that 

 chemistry was in before the dawn of physical chemistry. 



Taken by itself the C0 2 -production of an ordinary 

 green plant shows a very close relation with temperature. 

 In the case of the cherry-laurel worked out by Miss 

 Matthaei and myself the respiration of cut leaves rises by 

 a factor of 2.1 for every 10° C. (See Fig. 5, Resp.) 

 This has been investigated over the range of tempera- 

 tures from 16° C. to 45° C. At this higher temperature 

 the leaves can only survive ten hours in the dark, and 

 their respiration is affected in quite a short time, but in 

 the initial phases the, C0 2 output has the value of .0210 

 gr. per hour and unit weight of leaf, while at 16.2 C. 

 the amount is only .0025 gr. C0 2 . Thus the respiration 

 increases over a range of tenfold with perfect regularity 

 solely by increase of temperature. No reaction in a 

 test-tube could show less autonomy. At temperatures 

 above 45° C. the temperature still sooner proves fatal un- 

 less the leaf is illuminated so as to carry out a certain 

 amount of photosynthesis and compensate for the loss 

 of carbon in respiration. Thus, with rising temperature, 

 there is at no time any sign of an optimum or of a de- 

 crease of the intensity of the initial stage of respiration. 



Here, then, on the katabolic side of metabolism we have 

 no grounds for assuming that ' ' temperature-stimuli ' ' are 

 at work regulating the intensity of protoplasmic respira- 



