200 



[March, 1010, 



FIBRES. 



SELECTION OP COTTON VARIETIES 

 FOR UNIFORMITY. 



(From the Agricultural News, Vol. 

 VIII., No. 198, November 27. 1909.) 

 It is a well-known fact that the intro- 

 duction of a good variety of cotton into 

 a locality often leads to the exhibition 

 of a large amount of diversity among 

 the plants, and that, in addition, they 

 may appear to possess very different 

 characteristics from those presented by 

 them in their old surroundings. This 

 effect has been shown, in Bulletin No. 

 159 of the Bureau of Plant Industry of 

 the United States Department of Agri- 

 culture, to be different from other types 

 of variation, such as the ordinary fluc- 

 tuating differences, changes due to 

 accommodation, direct effects of en viron- 

 ment, and diversity due to hybridi- 

 zation, and is there termed a ' new-place 

 effect.' The remedy suggested is selec- 

 tion for 'local adjustment,' that is 

 selection for uniformity by rejecting all 

 lines of descent in which changes from 

 the best type occur ; it is a natural con- 

 comitant of selection for improvement, 

 and it seems that any properly organized 

 scheme for this would automatically 

 include it ; thus its consideration only 

 forms another argument for the con- 

 tinuous practice of selection. As many 

 of the conclusions reached in the above- 

 mentioned bulletin are applicable to 

 West Indian conditions, they are given 

 here : — 



The growing of a variety of cotton in 

 a new locality is likely to bring about a 

 distinct reduction in the yield, as well as 

 in the quality, of the fibie. This 

 deterioration has been found to be 

 connected with an increase of diversity 

 among the individual plants. Even 

 when a carefully selected, uniform stock 

 is used for the experiment, a much 

 greater amount of diversity may appear 

 in a new place than when the same 

 stock is grown under the accustomed 

 conditions of the previous locality, 

 where the variety was improved by 

 selection, 



The diversity that reappears in the 

 first season, when a variety of cotton is 

 grown in a new place, can be greatly 

 reduced in later seasons by selecting 

 seeds from the plants whose character- 

 istics have been least disturbed by the 

 transfer to the new place— those that 

 are the most fertile and have the best 

 lint. This process of selection to restore 

 the uniformity of a variety in a now 

 place is called local adjustment. 



Selection for local adjustment is 

 distinct in objects and methods from 

 breeding for improvement or for origin- 

 ating new varieties. The object of 

 local adjustment is to preserve varieties 

 already existing and to guard them 

 against recurrence of diversity. Prac- 

 tical advantages can be secured by 

 simple selection for local adjustment 

 without the separate testing of indi- 

 vidual lines of descent, as is required in 

 breeding for improvement of a variety, 

 or when new breeds are to be developed. 



The phenomena of local adjustment 

 are of general scientific interest as illus- 

 trating one of the influences of external 

 conditions upon the expression of charac- 

 ters in organisms. The recurrence of 

 diversity in a previously uniform variety 

 serves with other facts to show that 

 ancestral diversities continue to be 

 inherited, even when their expression is 

 avoided by efficient selection. That 

 changes of conditions can iuduce a return 

 to diversity shows that the environment 

 is able to influence the expression of 

 characters, and that its influence is 

 not limited to characters that vary 

 directly and regularly with changes of 

 environment. 



Apart from the effects of conditions 

 which limit or inhibit the growth of the 

 plants, two kinds of changes are found 

 to follow transfer to new places : (1) 

 Changes of accommodation to different 

 conditions, and (2) diversification, or Iosj 

 of uniformity. Changes of accommo- 

 dation do not directly increase diversity, 

 for they are shared by all the in- 

 dividuals, but changes of accommodation 

 are often accompanied by changes of 

 other characters which render the indi- 

 vidual plants much more unlike than 

 before. 



It is not necessary to believe that the 

 diverse characteristics that appear in 

 the new place come into the plants from 

 the external environment, or that they 

 represent direct effects of the environ- 

 ment upon the plants. It is more 

 reasonable to suppose that new con- 

 ditions induce diversity in an indirect 

 manner by disturbing the process of 

 heredity, and thus allowing ancestral 

 characters that had been transmitted in 

 latent form to return to expression, or 

 characters previously expressed to 

 become latent. Recurrence of diversity 

 may be quite independent of hybridiza- 

 tion, although some of the results are 

 very similar. 



The phenomenon of local adjustment 

 only strengthens the many other 



