88 



Carbon Assimilation. 



Table XIV. 



Relation between Assimilatory Activity and Number of Chloroplasts. 



But of course there is no evidence or even probability that all 

 chloroplasts contain the same amount of ehlorophyll, so that this 

 attempt to correlate assimilatory activity with quantity of chloro- 

 phyll is extremely crude. 



While we have no criticisms to offer in regard to Willstatter's 

 chemrcal analysis of the pigments, it appears from his preliminary 

 account that the experimental arrangements in his assimilation 

 experiments may be open to considerable criticism. As, however, 

 he promises a detailed paper in which " many remarkable details 

 in the experimental arrangement" are to be described, it seems 

 desirable to defer such criticism to a later period. 



The main principle of his method of experimentation is the 

 same as that used by earlier workers, e.g., Kreusler (1885-1890) 

 and Blackman. The noteworthy features of Willstatter's method 

 are : 



(1) The carbon dioxide is determined by weight in an absorption 

 apparatus. 



(2) The high intensity of illuinination. He uses a J watt Osram 

 lamp of 3000 candle power at 15-25 cm. distance from the leaf 

 chamber (corresponding to a light intensity of 48,000 to 130,000 lux). 



(3) The rapid stream of carbon dioxide (4-5 litres per hour). 



(4) The method of temperature measurement. The temperature 

 of theg-as in the leaf chamber is measured (presumably by a mercury 

 thermometer) ; it is obvious, in view of Blackman's experiments, 

 that this is indeed very unsatisfactory, particularly when such high 

 light intensities are employed. 



The experimental conditions used by Willstatter are such " that 

 the assimilation of a normal well assimilating leaf cannot be increased 

 by increasing the carbon-dioxide concentration or the light intensity" 

 The temperature, which is kept constant, generally 25"C, is 

 " favourable to assimilation." 



