A STUDY OF SEMI-STERILITY 



Hybrids with Half their Pollen and Ovules Sterile — Semi-Sterility Inherited 



in Half of the Second Generation — Progeny of Fertile Plants Remains 



Fertile — Progeny of Semi-Sterile Plants is Half Fertile 



and Half Semi-Sterile — A Demonstration of Gametic 



Segregation — A Theory of Semi-Sterility. 



John Belling, 

 Florida Agricultural Experiment Station, Gainesville, Fla. 



HYBRIDS between two allied 

 species of plants are often 

 partially sterile. In three hy- 

 brids I have completed an 

 investigation of the exact degree of 

 such sterility, and of the inheritance 

 of such an exact degree of sterility in 

 the succeeding generation's. I have 

 found what I regard as proof of the 

 causing of a definite degree of sterility 

 by the segregation of Mendelian factors 

 among the pollen-grains and embryo- 

 sacs, and the consequent abortion of a 

 definite percentage of these} The fol- 

 lowing brief description of the results 

 may, I hope, be of use to plant breeders. 

 The plants crossed were species of 

 Stizolobium. The Florida Velvet 

 "bean" (5. deeringianuni) was crossed 

 (both ways) with the Lyon "bean" 

 (5. niveiim) a variety introduced from 

 the Phihppines, and the fifth filial 

 generation (F5) has been grown. The 

 Velvet bean was crossed with the 

 Yokohama bean (5. hassjoo), and the 

 second filial generation (F2) has been 

 investigated. The Velvet bean was 

 also crossed with the China (or Chinese) 

 bean (5. niveum var.), of which cross 

 only the first generation has yet been 

 studied. Fig. 5 is a photograph of typi- 

 cal five seeded pods of the Velvet, Lyon, 

 Yokohama, and China beans. When 

 seeds are missing in these pods, this is 

 usually due to the ovules dying before 



maturity, and not to the abortion of 

 embryo-sacs. 



FIRST GENERATION HYBRIDS. 



The hybrid plants resulting from 

 these crosses were all similar in one 

 important respect, namely, semi-steril- 

 ity. Though the pollen-grains of the 

 four parent plants are, under normal 

 conditions, all sound; though their 

 ovules have normally perfect embryo- 

 sacs; yet this was not the case in the 

 Fl hybrids. The fiowers of these 

 hybrids had uniformly one-half of 

 their pollen-grains quite empty and 

 collapsed, and one-half of their ovules 

 had no embryo-sacs. In the Fl hybrid 

 of the Velvet by China, counts gave 

 3917 perfect pollen-grains to 3388 

 empty grains. Some of the empty 

 grains are often hidden under the fiill 

 ones, or swept to one side by the 

 liquid in which the pollen is spread 

 under the microscope, so that it is 

 probable that the number of empty 

 grains is larger than the actual count. 

 Fig. 5a is a photograph of the pollen. 



Counts of ovules in sections of 18 

 ovaries, from flowers of the same 

 hybrid, gave 50 ovules with embryo- 

 sacs, to 49 oviiles with aborted embryo- 

 sacs, proportions which were confirmed 

 by examination of the pollen and ripe 

 pods of the other hybrids. The empty 

 pollen-grains were uniformly mixed 



1 Detlefsen's valuable investigation in American Breeders' Magazine, III. 4, pp. 261-5, of the 

 inheritance of sterility in crosses and back-crosses between the guinea-pig and a wild Cavia, may, 

 I think, be explained on the hypothesis of the segregation of factors among the spermatozoa, and 

 the consequent abortion of those spermatozoa with certain factorial combinations; but I do not 

 know whether this can be scientifically proved from the data. 



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