stout: pollinations in CICHORIUM INTYBUS 337 



The term physiological incompatibility may well be used to 

 refer specifically to such cases of sterility in plants as Jost and 

 Correns have assumed are due to individual stuffs or to line 

 stuffs in which the stigma secretions are said to inhibit rather 

 than to stimulate the growth of certain pollen tubes, or to cases 

 where egg cells and sperms do not usually unite in self-fertilization, 

 as reported in the hermaphrodite animal Ciona intestinalis (Castle 

 '96, Morgan '04, '10, '13). 



While sterility due to physiological incompatibility is most 

 clearly in evidence when there is no anatomical incompatibility of 

 sex organs, it no doubt also exists in connection with anatomical 

 differences in numerous cases of interspecific sterility. 



III. Embryo abortion. — Sterility due to degeneration and death 

 of embryos during various stages of their development and quite 

 subsequent to an apparently normal fusion of germ cells is com- 

 mon, as illustrated in varieties of the apple (Kraus '15), in certain 

 hybrids of tobacco (Goodspeed '15), and in various Oenotheras 

 (Davis '15<2, '156). Goodspeed ('15) has used the term "pheno- 

 spermy" in describing empty seeds produced "either with or 

 without pollination." While the term is etymologically correct 

 in its reference to the seed as a sperm, the term may be misleading 

 to zoologists. Also there may well be many cases of abortion 

 that do not even lead to the production of seed-like structures. 

 It seems best to the writer to use the expression "embryo abor- 

 tion" for all cases of degeneration during the growth of the 

 embryo. Except in cases of the development of embryos by 

 apomixis all such cases would imply fertilization. 



No doubt all such cases of embryo abortion are fundamentally 

 due to physiological causes and that many such involve quite 

 local intercellular physiological conditions, especially in the cases 

 of seed sterility that accompany the development of large fleshy 

 fruits in which, as Kraus ('15) has pointed out, there are "varying 

 degrees of interdependence of seed and flesh formation," and that 

 from the standpoint of fruit-growing a distinction should be made 

 between self-fertility (seed production) and self-fruitfulness (fruit 

 production). Aside from the relations of seed and flesh formation 

 there is abundance of evidence that sterility and unfruitfulness 

 may both result in many fruit crops (Waite '95, for pears; Lewis 

 and Vincent '09, for apples; Backhouse '11, for plums; Gardner 



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