stout: pollinations in cichorium intybus 353 



All these cases are especially interesting in showing that self- 

 sterility may be so strongly persistent in large numbers of offspring 

 propagated vegetatively that in practical fruit production proper 

 pollinizers are necessary. In the cases of intervarietal sterility 

 reported by Gardner, we see a phenomenon quite identical with 

 that which Correns reports, almost simultaneously, in Cardamine, 

 in which the possibility of cross-sterility between sister plants of a 

 seed progeny was proven and the interrelations of sterility studied 

 in a pedigreed seed progeny. 



The studies made by Correns ('12, '13) places the emphasis 

 on the phenomena of cross-sterility which he made the basis of a 

 theoretical explanation of sterility (due to physiological incom- 

 patibility), which is decidedly different from that announced by 

 Jost. 



Correns ('12, '13) successfully crossed two self-sterile plants 

 of Cardamine pratensis which he had obtained from different 

 localities. The sixty plants reared from this cross were, Correns 

 states, completely self-sterile, although in his tables it appears 

 that at least one of them did set seed to self-pollination. These 

 plants exhibited all degrees of incompatibility when crossed among 

 themselves and with their parents. Correns attempts to explain 

 the phenomena of both self- and cross-sterility observed in Carda- 

 mine by the assumption of chemical substances, which he calls 

 "line stuffs" and which he assumes are represented in germ cells 

 by units which segregate in germ-cell formation. This is a real 

 attempt to solve the problem of the nature and the inheritance of 

 physiological self- and cross-incompatibility and hence deserves 

 most careful consideration, especially as it represents perhaps the 

 best Mendelian interpretation that is possible. 



The sixty sister plants derived from the cross between plants 

 designated as B and G when pollinated with pollen of these parents 

 fell into four classes: some were sterile to pollen of B and G, and 

 Correns hence concludes these have the constitution BG', some 

 were fertile with pollen of B, but sterile to pollen of G, and these 

 have the constitution hG\ plants fertile to pollen of G and sterile 

 to B, have the constitution Bg, and those fertile with pollen of 

 both B and G have the constitution bg. The parent plants are 

 hence assumed to form four kinds of gametes with respect to the 

 line stuffs involved; thus B produces gametes B and b, while G 



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