28 



filled with oxygen at the end. This gas would be given 

 ofF in bubbles at the eut end. However it should be 

 noticed that as soon as gaseous oxygen is emitted in thèse 

 spaces, COo-laden water is pushed away from the interior 

 cell-walls. In this way it is made compréhensible that an 

 auto-regulation of the COo-assimilation takes place and 

 that this is but little influenced by a rise of température. 

 This view also explains the slower assimilation stated at 

 the beginning of the experiments, because some time will 

 hâve to elapse before the protoplasm, the cell-walls and 

 the water in the intercellulars are saturated with oxygen. 

 Moreover the proportionality between velocity of assimi- 

 lation and intensity of light stated by us for light of less 

 than 2000 candies cornes in another view. For in light 

 of less than 2000 candies we must consider that the auto- 

 regulating action, referred to, will not occur. It is therefore 

 very probable, that this auto-regulation is caused by the 

 fact that the velocity of assimilation at a higher intensity 

 of light has increased at such a rate that the deposit 

 of gaseous oxygen into the intercellulars takes place, 

 whilst this did not occur at a lower intensity. However 

 this considération renders doubtful the opinion, that the 

 intensity of light could play the part of a limiting 

 factor, which one would feel inclined to draw from our 

 results in § 4. 



Though the explanation mentioned above is to a cer- 

 tain degree hypothetical, yet it foUows, that physical factors 

 play a part in the experiments with He/odea-shoots. So 

 it is very improbable, that the real assimilation-rate was 

 measured. A similar conclusion may be drawn from many 

 experiments of other investigators. Therefore one has to 

 conclude, that only assimilating organisms of a very simple 

 structure without intercellular spaces are fit for thèse kind 

 of experiments. 



