JOSEPH KRAFKA., JR. 



209 



temperature control were at hand several experiments were planned 

 to test the action of that factor on development. Culture bottles, 

 fitted up in the ordinary manner, were inclosed in humidity cases, 

 one in which the humidity remained practically constant at 35 per cent, 

 while the other was set for 60 per cent. Little or no difference was 

 noted in the rate of development, or in the facet count (Table III). 

 Direct evaporation was next tried. Ordinary culture bottles were 

 fitted with cork stoppers. A piece of glass tubing, extending through 

 the cork to the surface of the banana, admitted air from the humid- 

 ity control pipes. Another short tube with a cotton plug permitted 



TABLE III. 



Effect of Humidity and Evaporation on Facet Number in the Ultra-Bar Mutant of 



Drosophila melanogaster* 



* Temperature 23.5-25°C. 



the escape of the air. The culture bottle, into which a stream of 

 35 per cent humid air was passed, dried up at the end of the 2nd 

 day and no larvae developed. The cultures into which 60 per cent 

 air was admitted dried out rather rapidly, but not before many of the 

 larvae had pupated. Some of these emerged from pupation at the 

 expected time but the majority was about 5 days late. The effect on 

 the facet count is striking both as to the mean and the range. The 

 upper range for the 23°C. stock counts is 39 ;i in this culture it has 

 gone to 49, which is even above the upper range for 20°C. Unfor- 

 tunately an atmometer test is impracticable, and no quantitative 

 measure can be applied to this factor. 



