222 



MIGRATION 



that aspection and anniiation are due to much the same factors in 

 both plants and animals. 



Time of Arrival in Relation to Sunspots. The hypothesis that 

 migrants return earlier at the time of sunspot minima was first ad- 



FiG. 52. — Number of sunspots and the time of anival of migratory birds, 



(After DeLury, 1923.) 



vanced by De Lury (1923), in consequence of a study of the records 

 kept by the Chandon family at IMontdidier, France, from 1794 to 

 1869. He found a periodicity in the arrival of birds and in rainfall 

 corresponding to the sunspot cycle of about 11.5 years (Fig. 52). 



