60 



Thus, a doubling of thc intensity of assimilation did nol appear 

 unlil llie (A)^ concentialion was increased seven-fold: probably 

 Ihe light acled as a limiling faclor in most of Ihe experiments. 

 In some experiments with Carpinus Betalas the assimilation at the 

 beginning rises almost proporlionally to the supply of CO.^. 



In more recent days the influence of 

 the CO2 concentiation has been exa- 

 mined by Brown and Escombk (1902;, 

 Treboux (1903), Pantanelli (1904), 

 and Blackman and Smith (1911). Brown 

 and Escombe's experiments are not very 

 numerous, but they show quite clearly 

 that with a CO,^ percentage in the air 

 of up to 15 times the normal the assi- 

 milation is approximately directly pro- 

 portional to the concentration. The ex- 

 periments of Pantanelli and of Black- 

 man and Smith, carried out with water- 

 plants (Elodea, Fontinalis), point in the 

 same direclion. O. Warburg's recently 

 published experiments (1919) with a 

 Chiorella-Vike green alga also show an 

 approximate proportionalitj' between the 

 addition of CO2 and assimilation, with 

 lower concentrations. Warburgs COg 

 curve, however, has not the form descri- 

 £ ^ ^ g ro !? b^tl hy Blackman, but is more like the 

 Fig. 4. Diagram showing the curve for a bimolecular chemical reac- 



influeni-e of different COg .supply jJon fci) above p. 57) 



upon the C0„ assimilation of ,, . ,• .• • 1 »i • 



,r ,. ", , , ... , My own investigations into the in- 



]\asturtiuTn palustre and \ lola '' 



tricolor at ' light. lluence of the CO 2 concentration upon 



the intensity of assimilation show that 

 the rule >direct proportionality» has here a rather wide applica- 

 tion. The production of carbohydrates can be multiplied many 

 times by means of the supply of (Ä)^. The limil for the rise in 

 the assimilation depends upon the light, and is sometimes reached 

 — even with a light-intensily of ] — at relatively low concentrations 

 of the carbon dioxide. Further, in accordance with Blackman*s 

 theory, the limit is in some cases reached suddenly, and with any 



