stout: pollinations in cichorium intybus 425 



important in proving the frequency of impotence of various types 

 and of embryo abortion, and is suggestive that much may be 

 learned from work with the Oenotheras regarding the causes of 

 these phenomena. 



Not a few investigators have attributed the degeneration of 

 microspores and macrospores to conditions arising from long and 

 intensive cultivation. Thus Osawa ('13) considers that such is 

 the case in Daphne, and Wakker ('96) has reported that cultivated 

 races of sugar cane show various grades of such impotence which 

 are not present in the wild or semi-wild races. In all such cases, 

 however, the proof that hybridization has not been involved, as 

 Jeffrey has pointed out for similar cases, is not conclusive. 



Attempts to influence or change the degree of impotence in the 

 case of almost completely impotent interspecific hybrids in tobacco 

 (Goodspeed and Ayres, '16) have thus far been negative, which 

 it would seem emphasizes the view that the causes of such im- 

 potence are intracellular and only subject to slight, if any, 

 influences from the general nutrition or physiology of the plant 

 as a whole. The results reported by Martin ('13) and of Westgate 

 and Coe ('15) indicate that a plant may be impotent with respect 

 to development of macrospores in one crop of flowers and potent 

 in another crop as a result, they assume, of a difference in water 

 supply determined by the season. Here, however, the impotence 

 is not, it appears, a degeneration, but a condition in which the 

 tissues of the pistil remain vegetative. Coit ('15) has, however, 

 reported that the degree of impotence of pistils in the Washington 

 navel orange is changed to some extent by climatic conditions. 



That impotence involving degeneration should often occur in 

 the reduction divisions and not in the innumerable somatic divi- 

 sions that precede, and that such impotent hybrids are often 

 vegetatively very vigorous, may indicate that after all the so- 

 called incompatibility may not involve chemical reactions so 

 much as more purely mechanical relations. It is clear that 

 fertilization may occur so far as cell and nuclear fusions are con- 

 cerned and that diploid and often decidedly heterozygous organ- 

 isms may continue life with vigor only to have the intranuclear 

 processes, mechanical or chemical, or both, break down during 

 the more intricate processes of spore formation. There is no 

 clue in such behavior to the conditions operating in the production 



