THE EXPLANATION OF SELF-STERILITY 



E. M. East. Biissey Institution, Forest Hills, Mass. 



I 



N A recent paper by C. W. Moore ^ on 

 the subject of self-sterility, several 

 ill-advised statements were made to 

 which attention should be called. 



The paper begins with the sentence: 



Several who have made a study of the 

 problem of the inheritance of self-sterility of 

 plants have obtained results which did not 

 point to any one definite manner in which 

 flowers act when self-pollinated. 



One might read into the meaning of 

 this statement either that there was 

 great difference of opinion regarding the 

 behavior of self-sterile jjlants or that 

 little was known regarding self-sterility 

 before the apjjearance of the paper under 

 discussion. As a matter of fact a great 

 many details regarding self-sterile plants 

 are known. Darwin dealt with the 

 matter at some length, and more 

 recently extended researches by Jost, 

 Correns, Comjjton and Stout have 

 appeared. The i^resent writer has also 

 investigated the subject rather minutely 

 although only preliminary reports of 

 the work have been published. As to 

 the gross facts, there is not a great 

 difference of opinion among the later 

 writers. Each has found that pollen 

 grains germinate after self-pollination 

 as readily as they do after cross-pollina- 

 tion, but that they grow more slowly, 

 and the present writer has determined 

 that the growth curves of self-pollen 

 tuVjes are approximately straight lines, 

 while growth curves of cross-pollen 

 tubes are similar to those of auto- 

 catalytic reactions. Each has found 

 that there is cross-sterility of the same 

 nature as self-sterihty. In other words, 

 the plants of a self-sterile race are not 

 only self -incompatible, but some com- 

 binations are cross-incomi)alible. The 

 differences of ojjinion come in inter- 

 pretation of these results, and these 

 differences are due largely, we believe, 

 to the fragmentary character of the 

 evidence. 



Moore founds an hypothesis by which 

 to explain self-sterility on the supposed 

 fact that self-tubes are greater in diam- 

 eter than cross-tubes. In fact this 

 seems to be the main thesis of his paper. 

 He says : 



. . . the greater width of the self-pollin- 

 ated pollen tubes of Tradcscantia is due to 

 the fact that the food supply is more favorable 

 to the nourishment of a sclf-jjollcn tube than 

 it is to a cross-pollen tube. On account of 

 the abundant food supply the pollen tubes 

 did not lengthen, but grew wider since they 

 were in a very favorable medium. By this 

 hypothesis it is possible to explain most of 

 the data here presented. . . . 



What Moore did was to measure siwrt 

 self-pollen tubes and long cross-pollen 

 tubes as he distinctly states on page 204. 

 Now if he had measured self-pollen 

 tubes and cross-pollen tubes of the 

 same length, as he should have done, 

 it is almost certain that he would have 

 found them to be of the same width. 

 At least this is the observation of the 

 writer on numerous pistils of three 

 different self-sterile species of Nicotiana. 

 Moore's main thesis, therefore, seems 

 to be based uj^on an improi)er observa- 

 tion. 



The second i)oint made in the paper, 

 involving a criticism of the present 

 writer, is similarly without foundation 

 He says: 



He [East] states that "all gametes having in 

 their hereditary constitution something differ- 

 ent from that of the cells of the mother plant, 

 however, can i)rovoke the jjroper secretion to 

 stimulate tlic jiollcn tube growth, reach the 

 ovary before the flower wilts, and produce 

 seeds." From this it may be inferred that 

 there may be an enzyme in the pollen grain 

 that in a cross-polHnation is able to induce the 

 stigma to excrete a stimulating substance so 

 that the i)ollen tube is able to grow. In a 

 self-pollination this enzyme is not alile to act. 

 However, if tliis were the case, when a few 

 cross-i)c)llen grains were placed on a self- 

 pollinated stigma, they would be expected to 

 germinate and cau.se the stigma to produce the 

 stimulating substance. Thus the pollen tubes 

 from the self-pollination would also benefit 

 bv tlie stinuilating influence and should b 



• JouKNAK OF Hkkf.ditv, viii, 20.V 207, 1917. 

 382 



