SUMMARY 121 



of season. The effect of a favourable season is therefore to 

 produce a simultaneous increase of the coefficients for 

 various factors. 



Summary 



In experiments on the effect of different concentrations 

 of C0 2 , the introduction of the different solutions into the 

 plant- vessel causes a mechanical disturbance which modifies 

 the normal rate of bubbling. This was avoided by a special 

 device. 



The effect of excess of C0 2 is to produce a narcotic or 

 a poisonous action. 



The general characteristic exhibited by the photosyn- 

 thetic curve in relation to C0 2 -supply is that it is straight 

 up to a concentration of about 8 mg. of C0 2 per ioo c.c. 

 Above this there is a turning-point, when the curve becomes 

 rounded and gradually approaches the maximum. The 

 upper part of the curve is never abruptly horizontal. 



The coefficient alters with the season. The average 

 coefficient in winter is 39-9 ; in spring it is nearly double 

 that in winter. 



