'5b 



THE AGRICULTURAL NEWS. 



Febeuaey 20, 1909. 



have become fixed, and by picking out such plants the 

 new varieties may be established. 



. • The economic importance of the knowledge that 

 hks now been demonstrated as to the simple and 

 systematic manner in which unit qualities are inheriteil 

 is apparent to everyone, and its effects on the work of 

 improvement of agricultural crops will, undoubtedly^ 

 be f;ir-reaching in the fiitarc. In the past this work 

 has had to be carried forwaid by the long-continued, 

 and frequently unsatisfactorj' method ol' .selection, but ' 

 now, given a knowledge of the Mendelian oi- unit 

 characteis of the varieties of plant niirlor consid.ei'<1.-in 

 tion, crosses can be niarle with a complete fore-know- 

 iedfe of the results, and the whole subject of inheri- 

 tance has been placed on a definite basis. Having 

 selected, from all the varieties at hand, the qualities 

 needed, the breeder will be able to combine these quali- 

 ties according to his will, and by suitable crossing, to 

 build up a plant or animal possessing the desired 

 characteristics. 



From this it will be seen that the first step 

 necessary is to determine what are the Jlendelian 

 characters of a given species of plant or animal. It is 

 here that the chief difficulties of the work lie, for the 

 complete analysis of the qualities of the individual lo 

 be dealt with is a very lengthy and teilious process. 

 Judicious and repeated crossing, with intelligent 

 interpretation of the results, is, of course, the only 

 method by which to approach the task, and this line of 

 investigation carried out for a few generations will 

 usually reveal some pairs of characteristics that are 

 transmitted in the way described. 



Interesting work in the breeding of plants on 

 Mendelian lines, and which promises to lead to valuable 

 results, is in progress at the Agricultural Department 

 of the University of Cambridge under the direction of 

 Professor R. H. Biffen, .-ind among the economic plants 

 under trial, c-hief attention has been given to the 

 wheat plant. The numerous crossing tests th.-it have 

 been made have now at least laid the foiind.-itions of 

 an accurate knowledge of the various unit characters 

 that occur in wheat. Among the iiualities of this 

 crop which c.\[)( riuient h.is shown to be transmissible 

 as pairs of Mendelian characters are red grain and 

 white grain, early and late ripening, heavy as opposed 

 to poor cropping capacity, glutenous grain and starchy 

 grain, and — probably most important of all — immunity 

 to rust disease and liability to this jiest. The 

 possibilities that may arise from the now ascertained 

 fact that resistance to rust is a Mendelian ' unit 

 character' will be evident when it is mentioned that the 



average annual loss to the world's wheat crop, as the 

 result of rust -attack, has been placed at over 

 £100,000,000. 



In Egypt, e.^periments of the same nature were 

 established some years ago with a number of native 

 varieties of cotton, and have now bee" continued for 

 several years. Probably the most valuable point that 

 has so fir been demonstrated in these trials is that 

 long lint and short lint form a pair of Mendelian 

 unit characters, the former being dominant. Other 

 pairs of qualities inherited in the same way are: lar^e 

 ISeed and small seed, fuzzy seeds and seeds with small 

 quantities of fuzz, yellow Hower and cream-white 

 flower, etc. 



From the e.xamples that have been quoted, it will 

 be seen that a desirable characteristic which the 

 breeiler would wish to combine with other qualities of 

 similar economic value, and permanently fix in 

 an improved plant, may be either ' dominant ' 

 or ' recessive. ' In the majority of cases so far 

 instanced, the desirable characteristic has been the 

 'dominant' unit of the pair, but immunity to rust in 

 wheat is a ' recessive ' character, to which liability to 

 the disease is the corresponding ' dominant.' It may 

 be pointed out that the work of the investigator is 

 made easier when the quality it is desired to fix proves 

 to be a simple recessive. This is on account of the 

 fact that plants showing the recessive character breed 

 true from the moment of their first appearance in the 

 second generation from the original parent plants, 

 while only one-third of those individuals which in the 

 second generation show the ' dominant ' quality wil{ 

 breed ti iie, and a further generation has to be raised 

 before the pure dominants can be picked out. 



The terms 'dominant' and ' recessive ' as applied 

 to a pair of Jlendelian characters may at first appear 

 to imply that the latter is inferior to the former in 

 some way. Id should be borne in mind, however, that 

 this is not the case, and that the terms relate only to 

 till' first generatioii of hybrids produced from the origi- 

 nal parents, where the fact that one characteristic (as 

 whiteness in the pea flowers first referred to) disappear.s 

 for the time being, accounts for the term ' recessive,' 

 while the opposing (piality of colour, which is ajiparent 

 in all the individuals of this generation, is referred to 

 as the 'dominant ' character. The quality of 'white- 

 ness,' however, as it appears in the flowers of a propor- 

 tion of the plants of the second generation, is pure, 

 fixed, and permanent, despite the fact that these plants 

 are the offspring of hybriil pe.i plants bearing 

 c;olour'jil ilowers. 



