Scientific Agriculture. 



50 



[January, 1912. 



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 pollination from some 

 other variety. Dr. Erwin Baur has 

 found indications that sell-sterility in 

 Antirrhinum may be a Mendelian reces- 

 sive, but whether this important sugges- 

 tion be confirmed or not, the subject is 

 worth the most minute study in all its 

 bearings. The treatment of this problem 

 will illustrate the proper scope of an 

 applied science. The economic value of 

 an exact determination 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 chaptei in the study of 

 life. It may contain the solution of the 

 question, What is an individual ? — no 

 mere metaphysical conundrum, 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 bresding 

 stock for the meat market, and of late 

 years the practice has also been intro- 

 duced in raising table poultry. Mr, G. 

 N. Collins, of the U. S. Department of 

 Agriculture, has recently proposed with 

 much reason that it might be applied 

 ia the case of maize. The cross is easy 

 to make on a commercial scale and the 

 gain in yield is striking, the increase 

 ranging as high as 95 per cent. These 

 figures sound extravagant, but from 

 what I have frequently seen in peas and 

 sweet peas, I am prepared for even 

 greater increase. But what is the in- 

 crease ? How much of it is due to 

 change in number of parts, how much 

 to transference of differentiation or 

 homoeosis, as I have called it— leaf-buds 

 becoming flower-buds, for instance— and 

 how much to actual increase in size 

 of parts ? To answer these questions 

 would be to make an addition to 

 human knowledge of incalculably great 

 significance. 



Then we have the further question, 

 How and why does the increase dis- 

 appear in subsequent generations ? The 

 very uniformity of the cross-breds 

 between pure strains must be taken as 

 an indication that the phenomenon is 

 orderly. Its subsidence is probably 



orderly also. Shull has advocated the 

 most natural view that heterozygosis is 

 the exciting cause, and that with the 

 gradual return to the homozygous state 

 the effects pass off. I quite think this 

 may be a part of the explanation, but I 

 feel difficulties, which need not here be 

 detailed, in accepting this as a complete 

 account. Some of the effect we may 

 probably also attribute to the combin- 

 ation of complementary factors ; but 

 whether heterozygosis, or complement- 

 ary action is at work, our experience of 

 cross-breeding in general makes it practi- 

 cally certain that genetic factors of 

 special classes only can have these pro- 

 perties, and no pains should be spared 

 in identifying them. It is not impossible 

 that such identification would throw 

 light on the nature of cell division and 

 of that meristic process by which the 

 repeated organs of living things are con- 

 stituted, and I have much confidence 

 that in the course of the analysis dis- 

 coveries will be made bearing directly 

 both od the general theory of heredity 

 and on the practical industry of 

 breeding. 



In the application of science to the 

 arts of agriculture, chemistry, the found- 

 ation of sciences, very properly and 

 inevitably came first, while breeding 

 remained under the unchallenged control 

 of simple common sense alone. The 

 science of genetics is so young that when 

 we speak of what it also can do we must 

 still for the most part ask for a long 

 credit ; but I think that if there is 

 full co-operation between the practical 

 breeder and the scientific experimenter; 

 we shall be able to redeem our bonds 

 at no remotely distant date. In the 

 mysterious properties of the living 

 bodies of plants and animals there is an 

 engine capable of wonders scarcely yet 

 suspected, waiting only for the con- 

 structive government of the human 

 mind. Even in the seemingly rigorous 

 tests and trials which have been applied 

 to living material apparently homo- 

 geneous, it is not doubtful that error has 

 often come in by reason of the individual 

 genetic heterogeneity of the plants and 

 animals chosen. A batch of fruit trees 

 may be all of the same variety, but the 

 stocks on which the variety was grafted 

 have hitherto been almost always semin- 

 ally distinct individuals, each with its 

 own powers of luxuriance or restriction, 

 their own root-system9, and properties 

 so diverse that only in experiments on a 

 colossal scale can this diversity be 

 supposed to be levelled down, Even in 

 a closely bred strain of cattle, though 

 all may agree in their " points," there 

 may still be great genetic diversity in 



