chairman's address. 591 



can be fixed, are through Mendelian analysis and the recent developments of 

 genetic science now reasonably clear, and with that knowledge much of the 

 breeder's work is greatly simplified. This part of the subject is so well under- 

 stood that I need scarcely do more than allude to it. 



A simple and interesting example is furnished by the work which Mr. H. M. 

 Leake is carrying out in the case of cotton in India. The cottons of fine quality 

 grown in India are monopodial in habit, and are consequently late in flowering. 

 In the United Provinces a comparatively early-flowering form is required, as 

 otherwise there is not time for the fruits to ripen. The early varieties are sym- 

 podial in habit, and the primary apex does not become a flower. Hitherto no 

 sympodial form with cotton of high quality has existed, but Mr. Leake has now 

 made the combination needed, and has fixed a variety with high-class cotton 

 and the sympodial habit, which is suitable for cultivation in the United Pro- 

 vinces. Until genetic physiology was developed by Mendelian analysis, it is 

 safe to say that a practical achievement of this kind could not have been made 

 with rapidity or certainty. The research was planned on broad lines. In the 

 course of it much light was obtained on the genetics of cotton, and features of 

 interest were discovered which considerably advance our knowledge of heredity 

 in several important respects. This work forms an admirable illustration of 

 that simultaneous progress both towards the solution of a complex physiological 

 problem and also towards the successful attainment of an economic object which 

 should be the constant aim of agricultural research. 



Necessarily it follows that such assistance as genetics can at present give 

 is applicable more to the case of plants and animals which can be treated 

 as annuals than to creatures of slower generation. Yet this already is a large 

 area of operations. One of the greatest advances to be claimed for the 

 work is that it should induce raisers of seed crops especially to take more 

 hopeful views of their absolute purification than have hitherto prevailed. It is 

 at present accepted as part of the natural perversity of things that most high- 

 class seed crops must throw ' rogues,' or that at the best the elimination of 

 these waste plants can only be attained by great labour extended over a vast 

 period of time. Conceivably thjat view is correct, but no one acquainted with 

 modern genetic science can believe it without most cogent proof. Far more 

 probably we should regard these rogues either as the product of a few definite 

 individuals in the crop, or even as chance impurities brought in by accidental 

 mixture. In either case they can presumably be got rid of. I may even go 

 further and express a doubt whether that degeneration which is vaguely sup- 

 posed to be attendant on all seed crops is a physiological reality. Degenera- 

 tion may perhaps affect plants like the potato which are continually multiplied 

 asexually, though the fact has never been proved satisfactorily. Moreover it 

 is not in question that races of plants taken into unsuitable climates do degenerate 

 rapidly from uncertain causes, but that is quite another matter. 



The first question is to determine whether a given rogue has in it any factor 

 which is dominant to the corresponding character in the typical plants of the 

 crop. If it has, then we may feel considerable confidence that these rogues have 

 been introduced by accidental mixture. The only alternative, indeed, is cross- 

 fertilisation with some distinct variety possessing the dominant, or crossing 

 within the limits of the typical plants themselves occurring in such a way that 

 complementary factors have been brought together. This last is a comparatively 

 infrequent phenomenon, and need not be considered till more probable hypotheses 

 have been disposed of. If the rogues are first crosses the fact can be imme- 

 diately proved by sowing their seeds, for segregation will then be evident. For 

 example, a truly round seed is occasionally, though very rarely, found on 

 varieties of pea which have wrinkled seeds. I have three times seen such seeds 

 on my own plants. A few more were kindly given me by Mr. Arthur Sutton, 

 and I have also received a few from M. Philippe de Vilmorin — to both of 

 whom I am indebted for most helpful assistance and advice. Of these abnormal 

 or unexpected seeds some died without germinating, but all which did germinate 

 in due course produced the normal mixture of round and wrinkled, proving 

 that a cross had occurred. Cross-fertilisation in culinary peas is excessively 

 rare, but it is certainly sometimes effected, doubtless by the leaf -cutter bee 

 (Megachile.) or a humble-bee visiting flowers in which for some reason the pollen 



