LEAKE AND RAM PRASAD 119 



(average mean temperature) for the months June — August, and in 

 Map C the Imes of equal rainfall for June to October. The similarity 

 between the direction of these lines and those indicated for equal 

 percentages of the cotton crop is somewhat striking. It seems to 

 follow that, as far as the United Provinces are concerned, the chmatic 

 (rainfall and temperature), rather than any other, conditions are 

 the principal factors in determining the percentage area of cotton 

 grown in the various districts. A problem of somewhat different 

 nature refers to the conditions affecting the area sown to cotton 

 in the different seasons. The statistical aspect of this problem has 

 been dealt with by Moreland (25), by whom also reference is made 

 to the aggregation of the crop into certain areas or cotton tracts. 



The Genus Gossypium and the Types used in the investigations. 

 The distribution of the genus Gossypium throughout ti'opical 

 and semi-tropical chmates is nearly universal, the cultivation of 

 the numerous forms extends back to the earhest times, and the 

 origin of these forms, as with so many agricultural plants, is lost in 

 antiquity. Owing, moreover, to the commercial value of the crop 

 and to the amount of attention which has been devoted to it 

 from the time that the fibre began to be used as the raw product 

 of an ever-increasing industry, the original limits of cultivation of 

 each form have been broken down so that at the present time it is 

 possible to find in such a country as India examples of all the larger 

 groups of the genus. In many cases the history of these intro- 

 ductions is wanting and the presence of the plant alone bears testi- 

 mony to the fact. In spite of this intermingling of types, however, 

 it is still possible to recognise two fairly marked groups of culti- 

 vated forms which may be termed the New and Old World groups 

 respectively. Perhaps the most constant character by which these 

 two groups can be distinguished is to be found in the bracts which, 

 in the former, are free and. in the latter, united. It is impossible 

 here to enter into a revision of the genus, though there is little doubt 

 that such a revision is necessary. Such revision can only be made 

 after personal study of all the forms in the field, opportunity for 

 which has not been forthcoming. As so conunonly occurs in plants 



