No. 578] 



SELF-STERILITY 



85 



ulate pollen tube growth and in all likelihood promote fer- 

 tilization, and that like hereditary complexes are without 

 such effect. One may then imagine any degree of hetero- 

 zygosis in a mother plant and therefore any degree of 

 dissimilarity between the gametes it produces, without 

 there being the possibility of a single gamete having any- 

 thing in its constitution not possessed by the somatic tis- 

 sues of the mother plant. From the chromosome stand- 

 point of heredity the cells of the mother plant are duplex 

 in their organization; they contain N pairs. The cells 

 of the gametes contain N chromosomes, one coming from 

 each pair of the mother cell ; but they are all parts of the 

 mother cell and contain nothing that that cell did not con- 

 tain. These gametic cells can not reach the ovaries of 

 flowers on the same plant because they can not provoke 

 the secretion of the direct stimulant from the somatic cells 

 of that plant. 



All gametes having in their hereditary constitution 

 something different from that of the cells of a mother 

 plant, however, can provoke the proper secretion to stim- 

 ulate pollen tube growth, reach the ovary before the flower 

 wilts and produce seeds. Such differences would be very 

 numerous in a self-sterile species where cross-fertilization 

 must take place; nevertheless like hereditary complexes 

 in different plants should be found, and this should ac- 

 count for the small percentage of cross-sterility actually 

 obtained. It must be granted that this hypothesis satis- 

 fies the facts, but that is not all. It is admittedly a per- 

 fectly formal interpretation, but from a mathematical 

 standpoint,— granting the generality of Mendelian inheri- 

 tance, — it is the only hypothesis possible that can satisfy 

 the facts. 



Let us now look into a few of the ramifications of the 

 subject. Examinations of the pistils that have been sec- 

 tioned after cross-pollination show a considerable varia- 

 tion in the rate of growth of individual pollen tubes, 

 though our curves of growth have been made by taking 

 the average rate of elongation. Is this variation a result 



