132 A. FRANKLIN SHULL 



While the highest percentage of male-producers is found as 

 before in the lowest degree of alkalinity, there is not the regular 

 decrease in the proportion of male-producers with increase of 

 alkalinity, such as was seen in the preceding experiment. As it 

 would not be practicable to rear the rotifers in much more alka- 

 line water, all that we may safely conclude is that if alkalinity 

 influences the proportion of male-producers it does so only to a 

 small extent. 



Influence of urea on the percentage of male-producers 



Experiment XXV. One line of rotifers was bred in a ?ro solu- 

 tion of urea, a control line derived from a sister individual was 

 reared in spring water. The experiment was performed twice, 

 A and B, in table 27. In A, the parents of both lines had been in 

 spring water before the beginning of the experiment; in B, both 

 had been in urea. This experiment seems to indicate that urea 

 in the water tends to reduce the proportion of male-producers. 



Influence of ammonium compounds on the percentage of male- 

 producers 



Experiment XXVI. Ammonium salts. Four sister individuals 

 became the parents of the four lines in this experiment, which 

 was performed in June, 1910. One line was reared in spring water, 

 the others in ammonium salts of the following strengths: tots 

 NH4CI, ^^0 NH4NO3, and ammonium carbonate 1 gram to 7500 cc. 

 of the solution. The carbonate was not computed in terms of 

 molecular solution, because the c.p. salt was not used. The sub- 

 stance used was probably what is known as the sesquicarbonate, 

 a mixture of the bicarbonate and the carbamate. Table 28 gives 

 the details of each line. 



All of these ammonium salts reduced the proportion of male- 

 producers, two of them to one-half the proportion obtained in 

 spring water, the other to one-third. The consistent results 

 from the three salts seemed to make a repetition of the experiment 

 with any one of them unnecessary. 



