Pomeroy: It varied. 



Chapman: One other question. I am wondering whether your production 



underwater in relation to light is really completely valid, be- 

 cause it is the quality of light rather than the quantity that 

 matters under water. Your whole spectrum changes with 

 depths. The usual technique, I think, when one is measuring 

 algal productivity under water, is to measure it in terms of 

 energy received rather than in terms of light intensity which 

 may be entirely misleading. I am just wondering what results 

 you would get under those circumstances if one measured it in 

 terms of light energy received. 



Pomeroy: I would like to hear some other opinions on that. I wonder if 



it is not a rather thin layer of water that we are talking about? 

 It is a meter or less. 



Chapman: Well, I think the spectral composition is supposed to change 



rapidly even within a meter. What one really ought to get at 

 I imagine is an action spectrum for your diatoms at the depth 

 of water in which you are operating. 



Odum: The photometer he has does cover the spectrum of the action 



of photosynthesis and judging by what precedent there would 

 be for diatoms there is no reason to think that there would be 

 a great difference between the kind of measurement you would 

 get with a photometer and the kind of action spectrum. One 

 would be perhaps straighter than the other but your orders of 

 magnitude ought to be the same. 



Moul: Isn't there a piece of work that shows that the other pigments 



in diatoms pick up energy from light in the position where 

 chlorophyll does not and that you would get a plateau of photo- 

 synthesis from diatoms. The work was done on the Pacific 

 coast. And you are using clear water - filtered water. 



Pomeroy: Yes. Filtered water. 



Moul: I do not think this makes much difference. 



Pomeroy: I do not really either, but I cannot satisfy the criticism because 



I do not have an action spectrum. I do not have an energy value, 

 just a light value. 



Odum: On the subject of light that is one of the main ideas you have 



advanced. Let's see if this is right first, that what controls 

 this is whether they are getting the right foot candles, say 

 800 or 1,000 foot candles. 



91 



