3 2 4 TEE POPULAR SCIENCE MONTHLY 



do not take place. It is likely that in so far as the increased pro- 

 ductivity of a domesticated form as compared with its wild original 

 depends on more frequent division, the increase is due to loss of inhibit- 

 ing factors. How far may this reasoning be extended? Again we 

 know that in several plants — peas, sweet peas, Antirrhinum and certain 

 wheats — a tall variety differs in that respect from a dwarf in possessing 

 one more factor. It would be an extraordinarily valuable addition to 

 knowledge if we could ascertain exactly how this factor operates, how 

 much of its action is due to linear repetition, and how much to actual 

 extension of individual parts. The analysis of the plants of inter- 

 mediate size has never been property attempted, but would be full of 

 interest and have innumerable bearings on other cases in animals and 

 plants, some of much economic importance. 



That in all such examples the objective phenomena we see are 

 primarily the consequence of the interaction of genetic factors is almost 

 certain. The lay mind is at first disposed, as always, to attribute such 

 distinctions to anything rather than to a specific cause which is invisible. 

 An appeal to differences in conditions — which a moment's reflection 

 shows to be either imaginary or altogether independent — or to those 

 vague influences invoked under the name of selection, silently post- 

 poning any laborious analysis of the nature of the material selected, 

 repels curiosity for a time, and is lifted as a veil before the actual phe- 

 nomena; and so even critical intelligences may for an indefinite time 

 be satisfied that there is no specific problem to be investigated, in the 

 same facile way that, till a few years ago, we were all content with the 

 belief that malarial fevers could be referred to any damp exhalations in 

 the atmosphere, or that in suppuration the body was discharging its 

 natural humors. In the economics of breeding, a thousand such phe- 

 nomena are similarly waiting for analysis and reference to their spe- 

 cific causes. What, for instance, is self-sterility ? The phenomenon is 

 very widely spread among plants, and is far commoner than most people 

 suppose who have not specially looked for it. Why is it that the pollen 

 of an individual in these plants fails to fertilize the ova of the same 

 individual ? Asexual multiplication seems in no way to affect the case. 

 The American experimenters are doubtless right in attributing the fail- 

 ure of large plantations of a single variety of apples or of pears in a 

 high degree to this cause. Sometimes, as Mr. W. 0. Backhouse has 

 found in his work on plums at the John Innes Horticultural Institu- 

 tion, the behavior of the varieties is most definite and specific. He 

 carefully self-fertilized a number of varieties, excluding casual pollina- 

 tion, and found that while some sorts, for example, Victoria, Czar and 

 Early Transparent set practically every fruit self-pollinated, others 

 including several (perhaps all) Greengages, Early Orleans and Sultan 

 do not set a single fruit without pollination from some other variety. 



