1342 INDUCTION PHENOMENA CHAP. 33 



tion of the induction period was not independent of light intensity; it in- 

 creased from 1.5 minutes at 1350 lux to 5 minutes at 10,000 lux (at 19° C). 



Aufdemgarten observed that the CO2 gulp disappeared in the presence 

 of 0.001 mole/1, cyanide: we will discuss this observation in part B (Sect. 

 2e), together with the effect of cyanide on fluorescence (which has been 

 studied much more thoroughly). The same observer found the gulp 

 to be absent from induction curves obtained with higher plants; but this 

 cannot be a general rule, since the gulp was observed by McAlister in ex- 

 periments with both Chlorella and wheat. Perhaps the leaves used by 

 Aufdemgarten had a high diffusion resistance, which prevented rapid fluc- 

 tuations of the carbon dioxide exchange in the leaf from affecting markedly 

 the concentration of this gas in the atmosphere. 



The gulp was also found by van der Veen (1949,^-^ 1950) in experiments 

 with grass blades, conifer needles and some algae; but in Chlorella (and 

 certain other algae, or at least in certain cultures of these algae) it is re- 

 placed (or submerged) by a carbon dioxide burst, first discovered by Emer- 

 son and Lewis (cf. below). 



In a second investigation (1939^), Aufdemgarten succeeded largely in 

 eliminating the rapid oscillations (caused by unsteadiness of the apparatus) 

 which marred the registration curves in figure 33.10. Using the same or- 

 ganism {Stichococcus bacillaris) he now studied the effect on induction of 

 pretreatment of the algae. He used: (a) organic nutrition in daylight, 

 which produced cells full of assimilates, in the form of oil droplets; (b) and 

 (c) inorganic nutrition in acid and alkaline medium, respectively; and (d) 

 starvation (inorganic medium in darkness). The (rather unexpected) 

 result (fig. 33.11a) was that the composition of the inorganic medium 

 proved to be of more decisive importance for the carbon dioxide gulp than 

 the alternative of nutrition or starvation. Ten days spent in darkness in 

 an organic medium had almost no influence on the shape of the induction 

 curve (compare a and c, b and d). On the other hand, the gulp was much 

 more pronounced in cells incubated in the acid Eiler medium (pH 5.8) than 

 in cells incubated in the alkaline Kolkwitz medium (pH 7.6) (compare a 

 and b, c and d). 



It remains to be proved that acidity, and not other differences in the composition 

 (such as the presence or absence of ammonia), was the decisive factor. This assumption 

 is, however, favored by observations on the importance of acidity for anaerobic induction 

 {cf. section 6). 



Figure 33.11a shows that, when the dark period was reduced to one 

 minute, the difference between the induction curves in the two inorganic 

 media disappeared, not, as one would be inclined to say at first sight, be- 

 cause of disappearance of the carbon dioxide gulp, but rather because the 



