4o6 



NATURE 



[July 25, 1918 



have, been put forward to explain these facts. The 

 practical plant breeder is not primarily concerned 

 with the theory of the subject ; the Mendelian fact 

 of grand importance to him is. that unit characters 

 do segregate, and that new combinations of these 

 characters can be made. 



It may be of interest, therefore, to consider 

 some of the more important results obtained in 

 regard to food-producing plants, and to indicate 

 some of the difficulties which may impede future 

 progress. Of food grains none is more important 

 than wheat. The most marked achievement in 

 wheat breeding is the production of a variety 

 resistant, if not entirely immune, to the fungous 

 disease known as Yellow Rust {Puccinia gluma- 

 rum), as a result of the discovery that resistance 

 to this disease obeys the Mendelian law of segre- 

 gation. Once this was established it became a 

 comparatively simple matter to transfer this char- 

 acter as an independent unit from the poor yielding 

 Russian wheat, "Ghirka," in which it was 

 found, to a wheat suitable to the conditions of 

 England. The variety "Little Joss," which was 

 "made" in this way some ten years ago, is now 

 well established in the Eastern Counties. 



The possible. economic value of this achievement 

 becomes apparent if the enormous yearly losses 

 caused by rust — perhaps not far short of lo per 

 cent, of the yield annually — are considered. 

 Another economic character that can be con- 

 trolled in the same way is stiffness of straw, 

 a matter .of importance in those parts of 

 the country, such as the Fens, where a 

 weak-strawed wheat becomes "laid" in wet 

 seasons. It is interesting to learn that a short, 

 stiff-strawed variety known as "Penman" has 

 recently been produced which is likely to be largely 

 adopted in the Fen country. But the possibility 

 of greater additions to the food supply of the 

 country is now in sight. It is well known that 

 wheat is commonly a slow-growing plant ; sown 

 in late autumn or winter, it is harvested in 

 August. Barley and oats, on the other hand, 

 come to maturity more rapidly, and need not be 

 sown until spring. There are, however, certain 

 varieties of wheat which can be sown in spring, 

 but, unfortunately, their yield of grain is consider- 

 ably less than that given by winter wheats. The 

 result has been that under the ordinary conditions 

 of farming in this country the area that can be 

 sown witTi wheat is limited to that not occupied 

 by a crop during winter. Barley and oats must 

 be grown after "roots " because the latter are not 

 completely off the ground until early spring. If, 

 then, it were possible to make a spring wheat 

 combining the character of early maturity with 

 a yield approaching that given by winter wheat, 

 the economic gain might be enormous, for, obvi- 

 ously, it would be in the interest of home food 

 production to curtail the area occupied annuallv 

 by barley. If, then, we could add to the existing 

 acreage sown annually with wheat only one- 

 quarter of the normal acreage under barley and 

 oats, we should add probably 20 per cent, to the 

 home-grown cereals available for human food. 

 NO. 2543, VOL. lOl] 



The possibility of making an improved spring 

 wheat dei>ends upon how far early maturity and 

 yielding capacity are found to segregate. Appar- 

 ently, there are indications that the former does, 

 but the problem in regard to the latter is complex, 

 depending for its solution on the clearing up of 

 the difficulties that are encountered in dealing with 

 quantitative characters, such as yield, as distinct 

 from qualitative characters, such as colour of 

 grain. 



The questions involved are obviously of great 

 economic importance, for it is the quantitative 



I characters that often determine the economic value 

 of a plant or animal. But it is not simply a 

 question of the universality of the Mendelian law. 

 If, as some geneticists hold, the inheritance of 

 quantitative characters is regulated by. a complex 

 of unit characters, the practical application of 

 Mendelian principles becomes exceedingly difficult, 



1 for with any number of characters, over three the 

 number of possible combinations of unit characters 

 becomes generally too large to handle. And the 

 difficulty, does not end there, for, owing to en- 

 vironmental fluctuation, the comparative genetic 

 behaviour of individuals cannot be disentangled, 

 and the plant breeder is consequently driven 



I to resort to purely empirical methods of 

 selection. Nevertheless, the fact that the 



■ exact nature of the laws regulating the in- 

 I heritance of quantitative characters is still obscure 

 ' may not .seriously impede the work of the prac- 

 tical breeder. In fact, it has been found in prac- 



I tice that, provided desirable qualitative characters 

 can be built up in the desired complex, the quanti- 

 tative characters may be susceptible of improve- 

 ment by selective methods of a more or less 



; empirical nature. 



But when all is said, scientific plant improve- 



' ment in Great Britain has made only a small begin- 

 ning, due, no doubt, in part to the general excel- 



■ lence of the varieties of economic plants now estab- 

 : lished in this country. The "Improvers " of agri- 

 ■■ culture and horticulture in the nineteenth century 



revolutionised the industry, and, as an outcome 

 of their activities and influence, British seedsmen, 

 largely by selective methods, effected very great 

 improvements in economic plants. It is only com- 

 paratively recently that this country has fallen 

 behind. Allusion may be made to the great ad- 

 vances achieved in Sweden as a result of the work 

 of the Svalof plant-breeding station. Denmark 

 also is forging ahead, but, curiously enough, pro- 

 gress has not been remarkable in Germany, owing, 

 perhaps, to the extraordinary cult of Darwinism 

 which prevails there, and the consequent belief in 

 the effectiveness of mass selection. In America 

 considerable progress has been made from a scien- 

 tific as well as from an economic point of view- 

 notably in producing a cotton immune to the 

 destructive Wilt disease. 



But if a striking object-lesson of the successful 

 application of new methods to plant production 

 is needed we must turn to India. ^ Dating from 



1 Report on the Progress of Agriculture in India for 1916-17. (Calcutta. 

 Supt. Govt. Printing, 1918.) 



