154 



HAROLD H. PLOUGH 



TABLE 4 



b — pr — c 



Control. . 

 Dextrose. 



per cent 



18.2 

 16.8 



X 2 = 3.1 - Probability 38 in 100. 



Iron salts 



The constancy of the strength of linkage was shown further 

 by allowing the Fi females to develop in food which had been 

 soaked in a solution of the iron salt, FeCl 3 . This was tried in 

 M/12,000 and M/120,000 dilutions with negative results. 

 There is some question, however, as to whether the method 

 permitted action of the salt on the developing larvae and pupae, 

 and therefore the summaries of the counts are not given. 



IV. THE EFFECT OF TEMPERATURE 



Preliminary experiments 



Increase in crossingover after both heat and cold. In sharp 

 contrast to this series of negative results are the striking positive 

 results given by testing the effect of extremes of temperature. 

 These tests were carried on at first by the same methods used 

 in the experiments described above. A set of Pi parents — 

 black-purple-curved being the recessive mutant stock used — 

 were placed for four or five days in the bottles labeled A, B and 

 C respectively. Series A was kept at room temperature, which 

 varied between 22°C. and 24°C. Series B was kept in a Cyphers 

 electric egg incubator — 'Electrobator No. 2' — at 31°C, which 

 is close to the maximum temperature giving fertile offspring, 

 and Series C was kept in a carefully regulated refrigerator at 

 about 13°C. Great care was taken to prevent undue variation 

 in temperature, and in all of the experiments a temperature table 

 was kept and the temperature for each series recorded morning 

 and evening. As was to be expected, the control table showed 



