No. 502] CHEMICAL MECHANICS IN LIVING PLANT 657 



tion, but we find what I can only regard as a purely phys- 

 ical-chemical effect. The numbers obtained by Clau- 

 sen 15 for the respiration of seedlings and buds at different 

 temperatures indicate a temperature coefficient of about 

 2.5 for a rise of 10° C. 



To this final process of katabolism there could be no 

 greater contrast than the first step of anabolism, the as- 

 similation of carbon by the protoplasm as a result of pho- 

 tosynthesis. We must therefore next inquire what is the 

 relation of this process to temperature. 



This question is not so simple, as leaves can not satis- 

 factorily maintain the high rate of assimilation that high 

 temperatures allow. The facts of the case were clearly 

 worked out by Miss Matthsei, 16 the rate of assimilation 

 by cherry-laurel leaves being measured from —6° C. to 

 + 42° C. Up to 37° C. the curve rose at first gently and 

 then more and more steeply, but on calculating out the 

 values it is found that the acceleration for successive rises 

 of 10° C. becomes less and less. Between 9° C. and 19° 

 C. the increase is 2.1 times, the highest coefficient 

 measured, and exactly the same coefficient as for respira- 

 tion in this plant, which in itself is a striking point, 

 seeing how different the processes are. (See Fig. 5, 

 Assimilation.) 



The decrease of the coefficient with successive rises is 

 a state of things which is quite general among non-vital 

 reactions. A critical consideration of the matter leads 

 one to the conclusion, however, that this failure to keep 

 up the temperature acceleration is really due to secon- 

 dary causes, as is also the appearance of an optimum at 

 about 38° C. Some of these causes, have been discussed 

 by me elsewhere, 17 and I hope to bring a new aspect of the 

 matter before the section in a separate communication. 

 The conclusion formerly come to was that probably in 

 its initial stages assimilation at these very high tempera- 



"Landwirtschaftliche Jahrbiicher, Bd. XIX, 1890. 



"Optima and Limiting Factors. Annal* of Botany, Vol. XIX, April, 



