FERTILIZATION PROBLEMS: A STUDY OF 

 RECIPROCAL CROSSES. 



M. B. CUMMINGS. 



In attempting to account for failure in the making of recipro- 

 cal crosses one faces a perplexing problem. The number of 

 cases in which reciprocal crosses cannot be made is small, when 

 compared with that of successful ones. It is not the number of 

 successes or failures, however, which gives the subject promi- 

 nence. It is not the fact of failure in one case and success in 

 another; but rather the reason for such failure. If we can cross 

 plant A with plant B, why can we not cross plant B with plant 

 A? What is the immediate cause for the refusal of certain 

 plants to cross reciprocally, and how does their refusal manifest 

 itself? To find a satisfactory answer to these questions is the 

 purpose of this investigation. 



I. Records of Previous Work. 



SOME IMPOSSIBLE RECIPROCAL CROSSES. 



No exhaustive list of supposed impossible reciprocal crosses 

 is attempted at this time, since a few cases will serve the purpose 

 of presenting the problem. Kolreuter 1 , during a period of eight 

 years, made repeated trials to secure reciprocal crosses with 

 Mirabilis jalapa and Mirabilis longfflora. He tried more than 

 two hundred times to fertilize Mirabilis longfflora by applying 

 pollen of Mirabilis jalapa, but without success. The pollen of 

 the former when applied to the stigma of the latter, however, 

 produced fertile seeds. The same difficulty is met with when an 



1. Cited by Webber and Swingle. Hybrids and Their Utilization in Plant- 

 Breeding, Yearbook Dept. Agr., 1897, p. 383. 



Note. This paper is part of an investigation which has been in progress for the 

 past 12 years by Professor W. M. Munson, Horticulturist to the Station, upon the 

 effects of pollination. Beginning with 1892, occasional reports of progress have 

 appeared in the bulletins and reports of this Station. The studies here reported 

 upon were conducted under Professor Munson's direction. 



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