MALE-PRODUCTION IN HYDATINA 543 



in Whitney's cultures, was due to the oxygen liberated by the 

 green flagellates as a by-product of photosynthesis." Likewise, 

 page 157, "We suspect * * * Whitney's conclusion that 

 the food conditions influence male-production is correct." All 

 that was insisted upon by the authors of these passages was that 

 (page 157) "all the factors obviously associated with Chlamy- 

 domonas in the cultures should be separately tested before any 

 residue of influence is assigned to nutrition." 



Two factors associated with Chlamydomonas in Whitney's 

 earlier experiments were 1) an initial difference in the chemical 

 content of the water and 2) dissolved oxygen produced during 

 photosynthesis. In this paper the former factor has been elimi- 

 nated and the second has been measured. After deducting the 

 measured elTect of the oxygen from the total effect of the green 

 organism used for food, there is a residual effect which it seems 

 fair to attribute to nutrition. According to the results of ex- 

 periments described in the foregoing pages, this residual effect 

 due to nutrition is at least several times as great as the effect of 

 the accompanying oxygen. 



SUMMARY 



Repetition of the experiments with an excess of dissolved 

 oxygen, in which the excess was obtained by saturating the 

 water with an atmosphere of which 60 per cent was oxygen, 

 showed that oxygen is a male-producing agent. The experi- 

 ments of Shull and Ladoff had demonstrated that a smaller excess 

 of oxygen (obtained from a 40 per cent oxygen atmosphere) 

 increased male-production, but left in doubt the effectiveness of 

 a 60 per cent atmosphere. Rather direct comparison of the two 

 concentrations of oxygen, in this paper, shows that there is little 

 difference between them. The lower concentration may, per- 

 haps, be a little the more effective in inducing male-production. 



The amount of oxygen dissolved in the water in these experi- 

 ments has been measured by the Winkler method. The cultures 

 which were first saturated with an atmosphere of which 40 per 

 cent was oxygen and were then enclosed in a vessel in such an 



