SELF-STERILITY 



In Some Cases Where a Plant Cannot Be Fertilized by Its Own Pollen, It Appears 



That the Pollen-Tube Finds a Very Suitable Medium for Its Food 



Supply, and Hence Does Not Grow Long Enough 



to Ensure Fertilization 



C. W. Moore 

 Department of Plant Breeding, Cornell University, Ithaca, N. Y. 



SEVERAL who have made a study 

 of the problem of the inheritance 

 of self-sterility of plants have 

 obtained results which did not 

 ]3oint to any one definite manner in 

 which flowers act when self -pollinated. 

 In this work the purpose was to try to 

 find some clue to the nature or cause of 

 self-sterility. Several different kinds 

 of plants that had been reported self- 

 sterile were grown, and the stigmas and 

 styles were examined. 



In order to avoid confusion, the term 

 "self-sterility" wall here be understood 

 to mean that the pollen of a flower is 

 not capable of fertilizing the ovules of 

 that flow^er, but that the pollen is capa- 

 ble of fertilizing the ovules of another 

 ])lant and that the ovules of the plant 

 are capable of setting seed when 

 pollinated with pollen from another 

 plant. Thus flowers which have either 

 pollen or ovules which are abortive 

 would not be confused with plants that 

 have self-sterile flowers. 



The kinds of plants that were used 

 w'ere Tradescantia, alsike clover (Tri- 

 folinni hybridum), alfalfa (Medicago 

 sativa), and the Shirley pop])y (Papaver 

 rhoeas) . The flowers from twelve plants 

 of Tradescantia were used. There were 

 three plants of T. occidentalism and nine 

 that were Fi generation hybrids from a 

 cross of T. occidentalis by T. pilosa. 

 On the twelve plants, eighty-three self- 

 pollinations w^ere made, but none of 

 them set seed. Twenty-six cross-pollin- 

 ations Avere made, and all of them pro- 

 duced seed. 



An examination of the styles of 

 twenty pistils that were cross-pollinated 

 showed ]jollen tubes running to the base 

 of the style. The pistils were examined 

 by crushing under a cover-glass. Then 

 a drop of 1% solution of gentian violet 

 stain was added. The pistil was left 

 in the stain for about one minute, and 

 then the excess of stain was washed off. 

 The pollen tubes could easily be dis- 

 tinguished since they contained many 

 small vacuoles and had no cross walls. 

 The stigmas of the self -pollinated flowers 

 showed good germination of pollen 

 when examined in the same manner; 

 however, the pollen tubes did not grow 

 down the style. The styles of thirty 

 self-pollinated flowers were examined, 

 and the longest pollen tube was found 

 to be 0.5 mm. in length. The style of 

 Tradescantia averages about 5.0 mm. 

 in length. Thus, apparently, the rea- 

 son for the self-sterility of Tradescantia 

 is due to the failure of the growth of the 

 pollen tubes after germination. 



A SIGNIFICANT DIFFERENCE 



The significant fact about the pollen 

 tubes from a self-pollination was that 

 they were much wider than those from a 

 cross-pollination. The average diameter 

 of fifty pollen tubes from the self- 

 pollinations was .0216 mm., while the 

 average diameter of fifty pollen tubes 

 from the cross-pollinations was but 

 .0144 mm. The measurements of the 

 pollen tubes were taken as close as pos- 

 sible to the pollen grain. Measure- 

 ments of the diameter of the pollen 



1 Paper No. 56 of the Department of Plant-Breeding, Cornell University. Read at the 

 thirteenth annual meeting of the American Genetic Association, December 27, 1916, in New 

 York City. The writer wishes to express his appreciation of the many helpful suggestions and 

 useful criticism received from Prof. E. E. Barker. 



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