594 TRANSACTIONS OP SUB-SECTION K. 



a little light already. We are well acquainted with a few examples in which 

 the genetic behaviour of these properties is fairly definite. We have examples 

 in which, when two varieties differing in number of divisions are crossed, the 

 lower number dominates — or, in other words, that the increased number is a 

 consequence of the removal of a factor which prevents or inhibits particular 

 divisions, so that they do not take place. It is likely that in so far as the in- 

 creased productivity of a domesticated form as compared with its wild original 

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

 tors. 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 rn 

 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 intermediate size has never been properly 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 inter-action 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 con- 

 ditions — 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 postponing any laborious analysis of the nature of the material selected, 

 repels curiosity for a time, and is lifted as a veil before the actual phenomena ; 

 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 

 tho body was discharging its natural humours. In the economics of breeding, 

 a thousand such phenomena are similarly waiting for analysis and reference to 

 their specific 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 fertilise the ova of the same individual? Asexual multi- 

 plication seems in no way to affect the case. The American experimenters are 

 doubtless right in attributing the failure 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 

 Institution, the behaviour of the varieties is most definite and specific. He 

 carefully self-fertilised a number of varieties, excluding casual pollination, 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 polli- 

 nation from some other variety. Dr. Erwin Baur has found indications that 

 self-sterility in Antirrhinum may be a Mendelian recessive, but whether this 

 important suggestion be confirmed or not, the subject is worth the most minute 

 study in all its bearings. The treatment of this problem well illustrates the 

 proper scope of an applied science. The economic value of an exact determina- 

 tion of the empirical facts is obvious, but it should be the ambition of anyone 

 engaging in such a research to penetrate further. If we can grasp the rationale 

 of self-sterility we open a new chapter in the study of life. It may contain the 

 solution of the question, What is an individual ?— no mere metaphysical conun- 

 drum, but a physiological problem of fundamental significance. 



What, again, is the meaning of that wonderful increase in size or in ' yield ' 

 which so often follows on a first cross? We are no longer content, as Victorian 

 teleology was, to call it a ' beneficial ' effect and pass on. The fact has long been 

 known and made use of in breeding stock for the meat market, and of late years 

 the practice has also been introduced in raising table poultry. Mr. G. N. 

 Collins, 1 of the U.S. Department of Agriculture, has recently proposed with 

 much reason that it might be applied in the case of maize. The cross is easy to 



1 Uuieau of Plant Industry, Bulletin No. 191, 1910. 



