THE PHENOMENON OF SELF-STERILITY 1 



PROFESSOR E. M. EAST 

 Busset Institution, Harvard University 



In both animals and plants in which the two sexes have 

 been combined in the same individual, cases have been 

 found where self-fertilization is practically impossible. 

 This gametic incompatibility has been called self-sterility, 

 although the term is hardly proper as applied to normal 

 functional gametes that may fuse with their complements 

 in the regular manner, provided each member of a pair 

 has been matured in a separate individual. 



In plants the phenomenon has been known since the 

 middle of the nineteenth century, in animals a correspond- 

 ing discovery was made in 1896 by Castle, the species 

 being one of the Ascidians, Ciona intestinalis. During 

 the eighteen years that have passed since Castle's dis- 

 covery, Ciona has been studied on a large scale by Morgan 

 (1905), Adkins (Morgan, 1913), and Fuchs (1914). The 

 botanists, however, have lagged somewhat behind ; for, in 

 spite of having been acquainted with self -sterility in 

 plants for over half a century, and having found over 

 thirty species where a greater or less degree of self- 

 sterility occurs from which to select material, very few 

 thorough investigations into the physiology of the subject 

 have appeared. 



The main facts regarding fertilization in Ciona intesti- 

 nalis are about as follows : 



1. Under uniform suitable conditions, individuals vary 

 in degree of self-sterility, it being exceptional to find an 

 animal that is perfectly self-sterile. 



2. Self-fertility has never equaled cross-fertility, though 

 the possibility remains that some animals may be self- 



1 Bead by title at the thirty-second meeting of the American Society of 



