77 



assimilation will ivinain constant, even whtn the amount 

 of COj is increasing further. Apparently assimilation is 

 from this point onwards independent of the amount of 

 available COj — in reality the amount of available radiant 

 energy acts as limiting factor. 



In the same way a great many conditions can aci as 

 limiting factors in physiological experiments ; and the 

 fact, that conditions are kept constant makes it ail the 

 more probable that they will act in this way. It is obvious, 

 that this fact has to be kept in view, else erroneous 

 conclusions will be drawn quite easily. Thus for instance 

 in the above mentioned case the conclusion is obvious 

 (and it has been arrived at by several investigators) that 

 above a certain limit a furiher increase of the amount of 

 COj available is of no further influence upon the assimi- 

 lation, while in reality this influence certainly exists, but 

 cannot be seen because of the amountof available radiant 

 energy acting as the limiting factor. 



We will now try to examine, whether in the présent 

 investigation limiting factors hâve played a part. Generally 

 speaking a limiting factor will be présent, when a rising 

 or falling curve quite suddenly becomes horizontal (cf. fig. 

 2 on p. 6). 



When we look at the thick line in Fig, 6 and 7, p. 58 

 and 60 (representing the présentation- time after one hours' 

 preliminary warming), we see a more or less horizontal 

 part between 25° C. and 35° C. Hère a limiting factor 

 might perhaps be supposed to occur. This being the case 

 there must be a factor at 30° C, which loses its limiting 

 powers after a longer stay at this température, i. e. changes 

 in such a way that it no longer counteracts a greater 

 intensity of the process. 



I do not know what this factor might be; perhaps we 

 could imagine of a larger amount of an enzyme being 



