338 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



'13, for cherries; and others) from pure physiological incom- 

 patibility. Some cases of seed abortion may involve general 

 constitutional weakness on the part of the mother plant or animal. 

 Still other cases of seed abortion may involve an incompatibility, 

 intracellular in action, between chemical or structural elements of 

 the two sex cells which fuse to give the double mechanism of the 

 cells of the new sporophyte as especially noted by de Wies ('10, 

 p. 258). The whole phenomenon of embryo abortion in its rela- 

 tion to the other types of sterility as noted above needs thorough 

 investigation, especially in respect to the extent and degree of 

 cytoplasmic incompatibilities that may exist between the egg and 

 sperm immediately after fertilization. 



It should be recognized that the total sterility observed in a 

 species may involve several or even all the types of sterility as 

 outlined above. This is the case, for example, in red clover 

 {Trijoliimi pratense). In this species (Martin, '13; Westgate and 

 Coe, '15), there is often impotence especially in the first crop in 

 that the female reproductive organs often remain vegetative; 

 there is anatomical self-incompatibility seen in the adaptations for 

 cross pollination, and there is physiological self-incompatibility in 

 the very marked self-sterility that is known to exist; there is embryo 

 abortion not only of the usual fluctuating accidental type, but in 

 the regular abortion of one of the two ovules of each ovary both 

 of which are said to be fertilized. In the Oenotheras, Davis 

 ('15a and h) has pointed out that "pollen sterility" or "pollen 

 abortion" is very marked and that "the total amount of sterility 

 both gametic and zygotic Is simply amazing" ('156, p. 13). He 

 also suggests that "some degree of pollen and ovule sterility must 

 be expected to result" if there is also selective fertilization. Here 

 the phenomena of impotence of various grades and of embryo 

 abortion and degeneration are clearly present and it Is suggested 

 that physiological incompatibility giving selective fertilization Is 

 also in operation. 



It is, however, sufficiently clear that typical cases of the various 

 classes here noted may exist more or less independently and that 

 they are quite distinct at least in the direct expression of the 

 contributing causes. 



The investigations here reported are concerned with a sterility 

 which involves physiological incompatibility, and I shall discuss 

 ospecially the literature relating to this class. 



