1354 



INDUCTION PHENOMENA 



CHAP. 33 



After the observations of van der Veen (1949^--) with needles and grass 

 blades have demonstrated a "carbon dioxide gulp" at the beginning of 

 illumination and a "carbon dioxide burst" after its end, in exact opposition 

 to the findings of Emerson and Lewis with Chlorella (and of Aufdemgarten, 

 1939^•^ with Stichococcus and Hormidium), van der Veen (1950) next used 

 his apparatus on Chlorella. For this purpose, a suspension of Chlorella 

 cells was spread over a piece of filter paper, and the gas stream passed over 



Time 



Fig. 33.13K. CO2 burst in Chlorella at different temperatures; 

 diaferometer record (after van der Veen 1950). 



it into the diaferometer. Contrary to his expectations, van der Veen found 

 a confirmation of Emerson and Lewis' results. Figure 33.13H shows the 

 difference between the induction phenomena in Chlorella and in a higher 

 plant (a leaf of dahlia). The same response as Chlorella was shown by 

 another species of Chlorococcales, Protococcus olivaceus. 



Figure 33.131 illustrates the effect of light intensity on the carbon di- 

 oxide burst, as observed by van der Veen in Chlorella. Figure 33.13K 

 indicates that the burst increases in prominence as the temperature de- 

 clines from 26 to 12° C. (in apparent contradiction to the manometric data 

 of Emerson). It reaches its maximum volume after several hours of dark- 

 ness. It is the same in air (+3% CO2) and in O2 (+3% CO2) ; in hydrogen 

 ^;also with 3% CO2) it is less prominent; a second, smaller gush was noted 

 in this gas a few minutes later. 



