488 J. MYERS 



under various conditions of ii^lit intensity, temperature, and CO2 partial pressure. 

 What can be predicted as to the type or size of cells that are used? 



Myers: I don't know any a priori reason to predict what this situation will be. 



Tolbert: Is there any relationship between photoperiodism in higher plants and 

 the dependence on light for cleavage of the larger Chlorella cells to smaller cells? 



Myers: That, of course, is the reason this point becomes interesting. All I can 

 say is that stimulation of cell division is accomplished by an amount of light 

 which is below the compensation point as determined by growth. It is too small to 

 make any significant contribution to carbon assimilation via photosvTithesis. 

 Furthermore, cultures of Chlorella vulgaris grown in the dark have remarkably large 

 cells and show unusual division phenomena. 



Tamiya: As Dr. Myers stated, we distinguished at the beginning of our life- 

 cycle studies only two types of cells: the smaller ones which we called dark cells 

 and the larger ones which we called light cells. But, since we investigated the 

 change of physiological activities occurring during the life cycle of algae, we found 

 the necessity for more detailed discrimination of developmental stages. Now we 

 distinguish two stages in dark cells ("nascent" and "active") and three successive 

 stages in light cells (stages 1, 2, and 3). The light cells at different stages are almost 

 the same in their size, but markedh^ different in their grade of ripening or their ca- 

 pacity for forming autospores when kept dark under aerobic conditions. Chloro- 

 phyll content and photosynthetic activity are highest in "active" dark cells and 

 lowest in the light cells at stage 2. On the other hand, the respiratory activity is 

 lowest in "active" dark cells and highest in the light cells at stages 2 and 3. I 

 think that the data presented by Dr. Myers may well be understood on the basis 

 of our observations. 



Pirson: I want to make a short remark on some of our experiments with 

 Chlorella. We put Chlorella (this was the Emerson strain, not the strain used by 

 Professor Tamiya) in light and dark — 12 hours dark and 12 hours light. In one 

 light period we had no cell division, only an enlargement of the cells, and in the 

 other light period it was found that a very extensive cell division occurred and the 

 cell size decreased. 



As long as the suspensions were very thin and the intensities very high, w'e got 

 a characteristic periodic response of photosynthesis independent of cell division. 

 It consisted of a regular decrease during the time of illumination. We believe, 

 therefore, that we have another periodic principle which may be related to that 

 observed by Professor Tamiya. But this holds true only in very thin suspensions, 

 where photosynthesis cannot be measured manometrically. We have to make these 

 determinations using the polarographic method. 



Wassink: I understand that your curve at the maximum of 130 volumes of 

 oxygen per cell volume per hour refers to experiments on light saturation. 



Myers : That is correct. 



Wassink : Have you determined whether anything happens to the quantum ef- 

 ficiency at that point? 



Myers : We have not determined quantum efficiencies. However, when a syn- 

 chronized culture of small cells is illuminated there follows a characteristic time 

 course in the shape of the light intensity curves of photosynthesis observed in 



