November, 1910,] 



421 



Plant Sanitation. 



the case, the work of the mycologist is 

 rendered considerably more difficult, 

 and it can hardly be a matter for wonder 

 that his advice is sometimes not directly 

 suited to the requirements of the agri- 

 culturist. Too much emphasis cannot 

 be laid on the importance of forwarding, 

 with all specimens for examination, the 

 fullest possible account of all circum- 



stances, however trivial that may shed 

 any light on the problem, as in this way 

 only, can a full and sympathetic under- 

 standing of any given case be arrived 

 at by his advisers, which will enable 

 the practical agriculturist to be in re- 

 ceipt of the best and most carefully con- 

 sidered recommendations. 



SCIENTIFIC AGRICULTURE. 



MENDELISM, AND ITS APPLI- 

 CATION TO STOCK-BREEDING. 



By A. B. Bruce. 



(Prom the Journal oj the Board of Agri- 

 culture, Vol. XVII., No. 4, July, 1910.) 



Signs are not wanting that the re- 

 searches in the science of heredity asso- 

 ciated with the name of Mendel are 

 awakening the interest of practical men. 

 The appointment of the leading expert 

 in Mendelian research to the Director- 

 ship of the Innes Institute at Merton 

 suggests that horticulturists, at any 

 rate, anticipate that practical results 

 are likely to follow the application of 

 the new methods to garden plants. 

 That agriculturists, too, are not behind 

 hand in recognising the value of the 

 new science, as applied to the plants of 

 the farm, is shown by the recent ap- 

 pointment of Professor Biffen as Botan- 

 ist to the Agricultural Society of Eng- 

 land. Professor Biffen's success in pro- 

 ducing new and valuable varieties of 

 wheat is now a matter of common 

 knowledge. 



The value of Mendelian methods, when 

 applied to the production of new varie- 

 ties of plants, is both theoretically and 

 practically beyond dispute, but the 

 application of these methods to the 

 breeding of animals stands on another 

 and different footing ; results of econo- 

 mic importance have not been achieved 

 so far, and it is still doubtful, theoreti- 

 cally, whether the new methods are 

 applicable to the problems in which 

 practical men are interested. Stock- 

 breeders as a rule, have not, up to the 

 present, devoted much attention to the 

 matter, and it would seem that the 

 mathematical aspect which finds a place 

 even in professedly popular accounts of 

 the theory, is an obstacle which, to some 

 minds, proves insurmountable. If, how- 

 ever, the facts, established by the 

 Mendelian school, will be dissociated 

 from the theories which have been 

 framed to explain them, there is nothing 



in the new science that the ordinary 

 reader need have any difficulty in 

 comprehending. 



In the first place, to clear the path, it 

 is necessary to point out that Men- 

 delian methods and discoveries are con- 

 cerned with, and confined to, the inheri- 

 tance of distinct and mutually exclusive 

 characters only. For example, a flower 

 is either coloured or white ; colour and 

 whiteness are example of such charac- 

 ters. Thus, the Mendelian can predict 

 what will happen when, say, a white 

 breed of rabbit is mated with a coloured 

 one ; he cannot predict the result of 

 mating a large animal with a small one ; 

 he can foretell the colour of the eyes of 

 the children of two blue-eyed parents ; 

 he is ignorant of the law determining 

 their height. Confining our attention, 

 then, to the inheritance of sharply 

 defined characters, of which colour will 

 serve as a type, the root principle of 

 Mendelism may be simply stated. It is 

 that many, if not all, such characters 

 behave as distinct units in inheritance, 

 and may be present (or absent) in the 

 offspring, dissociated from the other 

 characters present in either of the 

 parents, in accordance with certain de- 

 finite numerical laws. For example, a 

 child may have the blue eyes of its 

 father, but all its other colour characters 

 from its brown-eyed mother ; moreover, 

 the Mendelian law enables us to affirm 

 that the blue-eyed child has no dark- 

 eyed character in its "blood," even 

 though its mother had dark eyes; in 

 other words the offspring of this blue- 

 eyed child, if mated with another blue- 

 eyed individual will never show any 

 "reversion" to dark eyes. It cannot, 

 however, be asserted that the offspring 

 of two dark-eyed parents will all have 

 dark eyes, for it is a fact that, whereas 

 the blue eyes are always "pure," in the 

 sense that it breeds true, the dark eye, 

 on the other hand, is sometimes pure 

 and sometimes impure, the " impurity " 

 consisting in the fact that the blue-eyed 

 character is sometimes latent and likely 



