266 THE BIOLOCY OF HYDRA : 1961 



MUSCATINE: I have no information on the algae in Chlorohydra 

 yet. But I have good data for Anthoplcura clcgantissima where one 

 can determine the biomass of the alga flora by using quantative 

 pigment techniques. 



GOREAU: You mean chlorophyll? 



MUSCATINE: Yes, and the various carotenoids. Using the 

 method of Richards with Thompson, and using cell counts and dry 

 weight data from pure suspensions of zooxanthellae, we find that 

 in Antlwpk'ura, the ratio of animal to algae on a dry weight basis 

 is about 332 to 1. 



GOREAU: Such data is very important in relation to turnover 

 studies. 



CLAYBROOK: How critical is the magnesium requirement for 

 Chlorohydra? Is this essential or does it merely increase the growth 

 rate? 



MUSCATINE: The maximum doubling time of green or albino 

 hydra is about 1.2 days. Without magnesium it is only 1.9 to 2.8 

 days. 



LENHOFF: I think it's important to add that they reqidrc mag- 

 nesium in order to grow. When we first received our Chlorohydra, 

 we could not grow them on any of our other culture solutions. The 

 last cation that we tried was magnesium. Then they doubled nearly 

 every day. 



CLAYBROOK: In our experiments with Chlorohydra, we don't 

 add any magnesium to the solution. 



MUSCATINE: Well, there is a possibility that they get enough 

 in their food, or perhaps you have a different strain of animals? 



CLAYBROOK: It could be. 



EAKIN: Although we have maintained our Chlorohydra in syn- 

 thetic solutions to which we have added no magnesium (solutions 

 which give optimal maintenance conditions for Hydra littoralis), we 

 find that the addition of Mg+ + decreases the doubling time and on 

 occasions has caused clones showing signs of depression to return 

 to normal. 



