THE ENVIRONMENT AND REPRODUCTION 27 



This experiment demonstrated conclusively the in- 

 fluence which increasing daylength has on the re- 

 productive organs of the junco. As Rowan remarked, 

 what had been done was to repeat on a small scale by 

 means of electric light what happens on a grand scale 

 when animals are transferred from one hemisphere to 

 the other. In both cases increasing light causes what to 

 the affected individuals is an unseasonal sexual develop- 

 ment. However, Rowan's experiment demonstrated 

 one other thing with startling clarity, namely the 

 complete lack of effect of temperature on the reproduc- 

 tive cycle of the junco. While this bird is accustomed to 

 breeding in the pleasant warmth of the Canadian spring, 

 these experimental individuals were sexually stimulated 

 in temperatures which fell progressively below freezing 

 point, to a minimum of - 46° C! 



Further experiments of the same kind were carried 

 out between 1925 and 1928^^2 using the junco and a 

 variety of other finches. These started with a study of the 

 effects of the intensity of illumination until an optimum 

 was found. After this it was possible to obtain complete 

 maturation of the gonads, with normal histology, in 

 spite of extremely low temperatures that continued for 

 long periods. As a further variation on this theme, 

 Rowan induced full maturation in a group of 30 juncos 

 in late autunm. Then he reduced their daylength from 

 15 hours to 9 hours, and so caused the gonads to regress 

 again. Finally, he exposed them to the normal increases 

 in daylength during late winter so that by May they came 

 into full breeding condition for the third time in twelve 

 months. 



Later these experiments were repeated using the 

 American crow, and essentially similar results were 

 obtained. 163, i64 About this time other workers were 

 attracted to this field, the first being Bissonnette.^i. 32 

 He studied the European starling in Connecticut, 

 U.S.A., and found that it too responds by gonad growth 

 to an increasing daylength in late autumn and early 



