- 228 — 



Corrections. Every estimation is reduced to the C0 2 content 

 of atmospheric air, viz. 0.55 mg perl, and to a temperature of 20°. 



The first of these reductions is carried out in the manner 

 described of Bkown and Escombe (1905 p. 41). It is supposed that 

 the C0 2 assimilation is proportional to the G0 2 content and that 

 the assimilation takes place at a G0 2 content that is the mean 

 between the G0 2 content of the air before and after it has passed 

 the leaf. For instance, when the G0 2 assimilation is 4 mg per 100 cm 2 

 per hour and the mean G0 2 content is 0.44, the corrected value is 

 4 x 0.55 

 0.44 = 5m g- 



The influence of temperature on the G0 2 assimilation is in- 

 vestigated by Matthaei (1904 p. 47). x ) In cherry-laurel the values 

 for the different temperatures were as follows (mg G0 2 assimilated 

 per 50 cm 2 per hour). 



Temperature, G 15 16 17 18 19 20 21 22 23 24 25 26 27 

 C0 2 assimil 6,1 6,5 7,0 7,5 8,0 8,5 9,1 9,7 10,3 10,9 11,5 12,1 12,8 



The shape of the assimilation curve is logarithmic; but it can 

 be made linear if instead of using the normal degrees we use another 

 scale obtained by reducing the value for the C0 2 assimilation for 

 20°, viz. 8.5, to 10 and the other values in the same manner. The 

 values of this scale (we can call tbem physiological temperatures) 

 are as follows: 



Temperature, C° . 15 16 17 18 19 20 21 22 23 24 25 26 27 

 Physiologic. Tp. . . 7,2 7,6 8,2 8,8 9,4 10 10,7 11,4 12,1 12,8 13,5 14,2 15,0 



The physiological temperatures can be used by reducing the G0 2 

 assimilation from a definite temperature to 20° C. Supposing that 

 we find a G0 2 assimilation of 4.4 mg at 18°, the value for 20° will 

 4 4 X 10 



be -^g-g — = 5 mg (supposing that the temperature influence the 

 assimilation in the plant in question in the same manner as in 

 cherry-laurel). 



Most of the experiments are carried out in conditions where 

 light acts as a limiting factor. According to Blackman only 

 one factor can act as limiting and a reduction of the estimations 

 to a definite temperature or G0 2 tension should therefore only 

 take place when one or other of these factors is limiting. Still 

 it is rather difficult to determine from the curves where these 



l ) Cf. also Brown, W. H. and Heise, G. W., Philippine Journ. of Science, 

 C, 12, p. 1, 1917. 



