stout: pollinations in cichorium intybus 409 



patibility, it would appear that the former is secondary to the 

 latter and involves quite the same processes. That the two are 

 not completely correlated is evident: plants of chicory that are 

 self-sterile may or may not be mutually cross-sterile, and any two 

 plants may exhibit different behavior when crossed with another 

 sister plant, quite as Correns' data show in Cardamine. Further- 

 more, self-fertile plants are found with degrees of fertility varying 

 from I to 70 per cent, which is quite analogous to the varying 

 intensities of cross-fertility. The evidence indicates that in these 

 cases cross-sterility is to some degree correlated with self-sterility. 



The sporadic and fluctuating nature of sterility resulting from 

 physiological incompatibility. — Darwin seems to have recognized 

 quite fully the fluctuating nature of this sort of 5e//-sterility at 

 least in its appearance among different plants of the same race. 

 His data, however, do not reveal such wide variations with various 

 degrees of self-fertility as I have found in chicory. Correns' data 

 show wide variations in the degrees of cross-fertility which, how- 

 ever, are ignored in his classification of results. Jost was fully 

 aware that plants only feebly self-fertile are frequent. In Ciona 

 different strains show different degrees of self-sterility. Neither 

 Darwin, Jost, nor Morgan was aware of the wide' variations 

 that may appear in the degree of cross-fertility of self-sterile plants. 



The behavior of sterility due to physiological incompatibility 

 in different species further emphasizes the fluctuating nature and 

 the marked individuality of the processes involved. Correns 

 from self-sterile parents obtained one class of self-sterile offspring 

 (though a few plants showed some indication of feeble self-fertility) 

 which exhibited all degrees of cross-sterility and cross-fertility 

 among themselves. East from self-sterile (?) plants of two 

 different species of Nicotiana obtained only self-sterile offspring 

 which, as far as tested, showed almost complete cross-fertility. 

 In Cichorium Intybus, I obtained from self-sterile parents some 

 self-fertile plants having the most sporadic and variable ex- 

 pressions of self-fertility and exhibiting all grades of cross-fertility 

 among themselves. The difiiculty of assuming that the causes 

 are identical in all these cases and due to the activity of any simple 

 chemical substances, either as to kind or intensity, is very evident. 



That there are quite different grades and degrees even of com- 

 plete self-sterility is indicated by the fact that two self-sterile 



