98 



THE AGRICULTURAL NEWS. 



March 30, 1912. 



self-fertilized. Further, in regard to self-fertilization, 

 the effect may be the failure to set fruit or the partial 

 development, only, of bolls; or seed may be produced 

 that gives rise to plants that are completely or partly 

 sterile, or show a lack of vegetative vigour. Actual 

 observations relating to these matters are given, which 

 show that all conditions may obtain; though even 

 with the same type of cotton, indications may appear 

 of the existence of an individual difference in the 

 degree of sterility induced by self-fertilization. It is 

 pointed out that a definite series of e.xperimenis is 

 required to determine the extent to which self-sterility 

 in the cottons is a function of the individual. 



The above considerations in regard to sterility 

 only take account of the phenomena shown by pure 

 types; the case remains of the similar circumstance 

 ■with respect to the offspring of a cross. Here, the 

 difficulty is increased; for the particular characters 

 shown may not only arise from the matters concerning 

 sterility dealt with above, but there may also exist 

 sterility resulting from specific or racial diversity. There 

 are not many observations available in regard to the 

 latter form of sterility; they go far enough to show 

 that the Indian forms of cotton are membars of a fairly 

 definite group, and that these members exhibit coni- 

 plets sterility when crossed with other forms; there is, 

 however, considerable divergence in the extent of fer- 

 tility when they are crossed among themselve?. The 

 complexity of the subject increases when attention is 

 given to the determination of the degree of sterility 

 that may be produced by such crosses; large and 

 inexplicable divergences of behaviour occur among in- 

 dividual plants of similar parentage. 



In dealing with the second part of the subject, 

 that is the frequency of cross-fertilization in the field, 

 the firtt matter to be considered is the mode of trans- 

 ference of pollen from one fiower to another. As is 

 well known the agencies most usually concerned 

 in this transference are the wind and insects, and 

 flowers often show adaptations by which they may most 

 readily take advantage of one or the ether of these agen- 

 cies. When it is considered in this way, the cotton Hower 

 shows little adaptation; and that, if anything, to cross- 

 pollination by insects. Further, the timoAvhich elapses 

 between the opening of the fiower and the advent of 

 the best chances for self-pollination is so short that it 

 leads to the suggesiion that cross-fertilization will not 

 be as, common as woulii appear to be indicated cy 

 a study of some of the characteristics of the fiower. 

 Observations on the great mixing of types occurring m 

 cottons growing in the field constitute, however, 



a strong argument for the frequent occurrence of cross- 

 fertilization, and this is supported by the significant 

 fact that the only types grown pure, in India under 

 ordinary conditions of cultivation, are those whose 

 natural habit helps to prevent the occurrence of cross- 

 pollination, ^lention is made of the very- divergent 

 views that have been held by various investigators as 

 to the extent to which cross-pollination takes place in 

 the field; the res'ults of the earlier observations on the 

 subject are contained in Sir George Watt's article on 

 Gossypium.* Froni a consideration of these and from 

 the results of much personal observation, this investiga- 

 tor concludes that hybridization has played a large part 

 in the history of the cotton plants of India, and he still 

 holds this view in a more recent work.+ The results 

 of experiments by other investigators are noticed in 

 the Memoir that is under present consideration, and 

 attention is drawn to the fact that Balls considers that 

 in Egypt at least 5 per cent, of cross-fertilizition takes 

 place yearly; there is also mention of work conducted 

 recently in the United States, from which it has been 

 concluded that, in North Georgia, the percentage of 

 cross-pollination is at least twenty, with strong prob- 

 abilities of forty per cent, of cr.'ss-pollination.;!: 



Det Ills of experiments relating to the subject are 

 presented in the Memoir, which show, in their broad 

 results, that several forms of Indian cotton have arisen 

 through natural cross-pollination. Consideration is 

 then given to the distance at which cross-pollination 

 may occur in the field — a matter of much importance 

 in cotton-breeding, and in the maintenance of definite 

 types in cultivation. Webbe:* considered that absolute 

 isolation would require separation of five to ten miles, 

 but that practical isolation needs a distance of a quarter 

 to half a mile. As far as has been possible to draw any 

 conclusions from experiments and observations in India, 

 it appears that such distances are unnecessary. The 

 particular conclusions reached are expressed as follows: 

 ' for practical purposes, there is no objection to culti- 

 vating different races in adjoining plots, provided the 

 two lines bordering the second race are discarded for 

 the purposes of seed supply. Additional security, and 

 one which might render even this precaution unneces- 

 sary, may perhaps be obtained by the separation of two 

 kinds with one or two lines of a crop which flowers 

 freely during the co*iton season, and will grow under 



* Dictionary of the Economic Products of India, pp. .^-42. 



f The Wild and Cult iv.-il I'd Cottons of the Worid, 1!)(37, 

 p. DO. 



lUee AiiiicuUnnd Neios. Vol. X, p. 102. 



"I Yearbook of the United States Department of Agricul- 

 ture, 1902, p. 370. 



