No. 596] SHORTEB ARTICLES AND DISCUSSION 493 



tor, surely we should expect that the true-breeding single, which 

 is SS in constitution, would be less vigorous still. It seems 

 somewhat gratuitous to suppose that the character singleness is 

 sometimes due to a factor S associated with greater vigor and 

 sometimes to a factor Si associated with diminished vigor; or, to 

 put it another way, to assume that if it is the lack of one dose of 

 the factor for singleness in the ever-sporting plant which makes 

 it less vigorous, that the lack of the double dose in the double 

 plant leads to the opposite result of greater vigor. Is it not 

 almost a certainty that the greater vigor of the double-flowering 

 plant is due to the fact that the energy of the individual is not 

 exhausted in the formation of the reproductive cells, but is ex- 

 pended in producing a more vigorous vegetative growth? And 

 hence that a check to vegetative growth, similar in cause and in 

 degree, is operative alike in the pure-breeding and the double- 

 throwing single? To obtain strict proof that this is so is diffi- 

 cult since it might always be argued that the particular pure- 

 breeding single strain used as a control was not precisely identical 

 in all other respects with the double-throwing strain with which 

 it was being compared. It can, however, be stated that in some 

 commercial material supplied as double-throwing, but which 

 proved to be a mixture of pure-breeding and ever-sporting 

 singles otherwise apparently identical, no indication was observed 

 of any difference in vigor between the two kinds of singles. The 

 second argument which Frost urges in support of his hypothesis 

 of differential sterility is the fact that the seeds (embryos) which 

 produce doubles have on the whole rather greater viability than 

 their sister seeds which give singles. But this second argument, 

 depending for point on the same entirely unsupported assump- 

 tion as that derived from vegetative habit, is open to the same 

 objection. I have never observed that the seed-producing true- 

 breeding singles showed any superiority as regards viability over 

 that yielding the ever-sporting singles, but rather, as with vege- 

 tative habit, that the distinction is to be drawn between any 

 kind of single-producing seed on the one hand, and double-pro- 

 ducing seed on the other. I have sown a large quantity of ap- 

 parently excellent seed of a pure-breeding single after the lapse 

 of some years and failed to get any germination, just as I have 

 failed sometimes to get any singles from old double-throwing 

 seed although a few doubles were obtained. Lastly, Frost brings 

 forward the somewhat out-of-date view that the percentage of 



