GENETICS 325 



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 

 any one 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 indi- 

 vidual ? — 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 breeding 

 stock for the meat market, and of late years the practise has also been 

 introduced in raising table poultry. Mr. G. 1ST. Collins, 2 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 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 this increase ? How much of it 

 is due to change in number of parts, how much to transference of dif- 

 ferentiation or homceosis, 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 

 disappear 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 at- 

 tribute to the combination of complementary factors; but whether 

 heterozygosis, or complementary action, is at work, our experience of 

 cross-breeding in general makes it practically certain that genetic fac- 

 tors of special classes only can have these properties, and no pains should 

 be spared in identifying them. It is not impossible that such identifi- 



2 Bureau of Plant Industry, Bulletin No. 191, 1910. 



