I2 4 RESPIRATION 



evolution of carbon dioxide, a result which is in accordance 

 with the observations of Blackman mentioned above. 



These observations are different from those made by Miiller- 

 Thurgau and Schneider-Orelli who observed a permanent in- 

 crease in respiration after due exposure to high temperatures, 

 whilst Kuijper found a decrease to obtain. This discrepancy 

 may be due to the fact that Kuijper's seedlings were subjected to 

 the increased temperature for a lesser time than the potatoes of 

 Muller-Thurgau and his collaborator, and, as has already been 

 remarked, the material employed was in active growth on the 

 one hand whilst on the other it was resting. Kuijper explains 

 his results on the hypothesis that there are two distinct pro- 

 cesses concerned in respiration which are affected differently 

 by a continuance of high temperature, one phase being early 

 depressed whilst the other is stimulated ; there is here a pos- 

 sible correlation with the dual origin of the carbon dioxide 

 of respiration, which, according to Palladin, arises from the 

 activity of an oxidase and of a carboxylase. Like Muller- 

 Thurgau and Schneider-Orelli, Kuijper recognizes the inter- 

 relation of temperature and the nature of the available res- 

 pirable material. Thus of the seedlings examined, the lupin 

 showed a rise in the respiration intensity from 15 C. to 20° C, 

 the pea from 20° C. to 25 C, and the wheat at 30 C. The 

 fluctuation period was well marked at 25 C, 30 C. and 35 C. 

 respectively, and the continual fall in carbon dioxide output 

 obtained at 25 C, 35 C. and 40 C. respectively. Of the 

 food available, the lupin has $7 per cent., the pea 22 per cent., 

 and the wheat 12 per cent, of protein, whilst of starch the 

 lupin has none, the pea 54 per cent, and the wheat 74 per cent. 

 If respiration be a purely chemical process, a combustion 

 of, say, sugar, van't Hoff's law should apply throughout the 

 process : the evidence shows, however, that the law is followed 

 only for lower temperatures ; at higher temperatures, as has 

 been seen, fluctuations occur and correlation comes to an end, 

 which is indicative of the intervention of internal factors, the 

 nature of which is not clearly understood. Clausen * found 



* Clausen : " Landw. Jahrb.," 1890, 19, 893. 



