stout: pollinations in cichorium intybus 411 



one to the full complement may be produced. Cases of persistent 

 low-fertility occur under the same conditions of chance experi- 

 mental error. In such cases few seeds are set in a head of similar 

 flowers all equally potent, and all seemingly subject to as nearly 

 equal conditions of nourishment as is possible. The differences 

 in compatibility exhibited by different flowers of the same head 

 to mixtures of the same pollen are identically the same in the 

 results (seed or no seed) as that seen in all the flowers in a head in 

 the case of complete self- or cross-sterility as compared wuth 

 marked high self- or cross-fertility. The differences can not be 

 due to lack of pollination, as the method used, especially in self- 

 pollinations, was equally ample for the distribution of pollen on 

 all stigmas. These considerations seem to indicate that modifica- 

 tions of the same processes that produce complete self-sterility 

 are also operating In the production of feeble self-fertility. 



Further evidence of the fluctuating and individual nature of the 

 processes and conditions involved in such cases may be gained 

 by comparing the results of geitonogamy with those obtained 

 by autogamy. The earlier experiments of Darwin ('77), Ulrich 

 ('02), and Jost ('07) indicate that geitonogamy may in some 

 cases be more productive of seed than autogamy. This ques- 

 tion has never been adequately investigated in cases of physi- 

 ological incompatibility where every sort of morphological in- 

 compatibility is eliminated. The results of Shaw ('16), indicate 

 that in the proterandrous sugar beet autogamous fertilization 

 is very nearly always sterile, while geitonogamous crossing is 

 often successful, especially if the flowers are from distant branches. 

 In these self-pollinations care was taken to preserve the pollen 

 of the proterandrous flowers for use at the time when the stigmas 

 were receptive, but it was not shown, however, that pollen of the 

 same age was more effective In geitonogamy. 



On the other hand, the marked persistence of self-sterility in 

 varieties propagated vegetatively as seen in such plants as the pear, 

 apple, plum, cherry, and blueberry is suggestive that the processes 

 are quite uniform not only in the parts of a single plant but in the 

 series of plants vegetatively derived from it. In such plants 

 there is especial opportunity to test the degrees of bud variation 

 and the relative fertility of plants of different lines of descent, 

 and thus obtain accurate data on this important point. Thus 

 far Such studies have not been made. 



