THE SELF-STERILITY PROBLEM 



Many Important Points in Fruit-Growing Still Await Explanation — Recent Progress 

 in the Study — Need of Distinguishing the Various Factors Entering 



into the Problem^ 



E. J. Kraus 

 State Agricultural Experiment Station, Corvallis, Ore. 



The entire question of the causes of 

 self-sterility quite generally in the plant 

 kingdom, and in orchard fruits espe- 

 cially, is largely in the speculative stage. 

 We are just beginning to bring together 

 a great body of facts from which, in 

 time, we confidently may hope to 

 deduce some of the real fundamentals 

 of the self-sterility problem. It should 

 be understood at the outset that some 

 of the statements made in this paper are 

 speculative and consequently should 

 not be regarded as conclusions. While 

 based upon a large amount of experi- 

 mental data they may be interpreted 

 eventually in some other way. 



DEFINITION OF TERMS 



First of all, it is necessary that there 

 be a clear understanding of certain 

 terms which often are applied more or 

 less indiscriminately. As used in this 

 paper, a distinction is made between 

 self -fertility, self-fertilization, and self- 

 fruitfulness. The term fertilization is 

 used in a strictly botanical sense; self- 

 fertilization further restricts all gametes 

 concerned to those derived from the 

 same individual. In the case of varie- 

 ties propagated vegetatively any so- 

 called individual of that variety still 

 would be considered as a mere part of 

 the one individual. Self -fruitful is used 

 to mean the ability of a plant to produce 

 mature fruit, either without pollination 

 (parthenocarpy) or when pollinated 

 with its own pollen, whether or not 

 fertilization takes place, or whether or 

 not seeds are produced. It has refer- 

 ence to the development of vegetative 

 parts only. A fruit tree, therefore, may 

 be self -fruitful and self -sterile, or self- 



1 Read before the twelfth annual meeting of the American Genetic Association, at Berkeley, 

 Cal.. August 5, 1915. 



549 



THE problem of the pollination of 

 horticultural fruits has been, 

 and is, a subject of great 

 practical importance, and of 

 much painstaking investigation. Never- 

 theless, results from carefully planned 

 and skillfully conducted experiments 

 frequently are so apparently contra- 

 dictory that when the whole body of 

 facts is considered, very few conclusions 

 seem warranted. In the past far more 

 has been concluded from the work of 

 two, three or even five years than can 

 be justified. The many questions which 

 arise, especially as they relate to the 

 sterility problem, will require, for their 

 solution, years of patient labor. Such 

 solution will not come from a mere 

 dusting of stigmas with pollen in the 

 springtime and an elaborate tabulation 

 of results in the fall. 



Still, the outlook is by no means dis- 

 couraging. Every recorded fact, no 

 matter how seemingly insignificant, is 

 to be regarded as a step in advance 

 even if for the moment it does seem 

 merely to contribute to confusion. 

 While it should be realized that a single 

 fact is more valuable than extended 

 interpretations of opinions based upon 

 hasty observations or limited data, yet 

 it is equally true that hypotheses are 

 often useful and stimulating, and make 

 for advancement in the understanding 

 of facts. It should be remembered that 

 they are hypotheses, and utilized as 

 such; it is when they are regarded as 

 hard and fast conclusions that they 

 become dangerous. The investigator 

 should be willing to discard hypotheses 

 that are clearly shown by facts to be 

 untenable. 



