-4'. 1 4 



THE AMEBIC AX X ATE HALLS T 



[Vol. L 



doubles is increased hy starvation treatment. Though this treat- 

 ment is still practised by German growers, it survives from a time 

 when it was not yet appreciated that the capacity of the individ- 

 ual to become a single or a double depended upon its inherited 

 constitution and not upon the effects of environment. It may be 

 pointed out that the French growers have been in the habit of 

 pursuing precisely the opposite method of treatment with the 

 same object in view. The inhibition of flowering which Frost 

 has observed to be more marked in the singles than in the doubles 

 in the case of one variety when subjected to a high temperature 

 does not seem to me to bear on the question at issue, 7 which is 

 whether there is any direct evidence of the selective sterility of 

 ovules and pollen in the ever-sporting as compared with the true- 

 breeding single. For I gather that Frost is not prepared to 

 maintain that sterility occurs regularly also in the pure- 

 breeding single as well as in the ever-sporting single. It is 

 further to be noted that besides assuming the definite sterility 

 of all the Si pollen in an individual of S x s constitution pre- 

 sumably producing equal numbers of and s grains, Frost 

 has to have recourse to the vague assumption that there is 

 only a slight tendency to selective elimination of the S x egg 

 cells out of a total composed presumably of equal numbers of 

 Sj and s. One is fain to ask on what grounds it is possible to 

 uphold the view that the same factor can destroy the func- 

 tional activity of every pollen grain carrying it, but is only 

 able to affect some of the egg cells in which it is borne? In 

 this connection it may be mentioned that it is no uncommon cir- 

 cumstance even when self-fertilization is left to nature to obtain 

 pods both in pure-breeding and double-throwing singles where 

 every ovule has been fertilized, and this can always practically 

 be ensured where fertilization by hand is carried out in good 

 weather. Though he instances no examples I gather from his 

 previous reference to Belling 's work that he has in view such 

 cases as that of Stizolobium deeringianum (the Florida Velvet 

 "bean") and other species investigated by that observer, 8 Nico- 

 tian a on which recent experiments in this connection have been 

 « The real advantage of the German method of treatment is that the seed 

 harvested is all well ripened. 



