64 STUDIES IN INDIAN TOBACCOS. 



types are allowed to flower and seed freely at Piisa, the uniformity 

 of the type is soon lost and the crop consists of a mixture of very 

 diverse forms. Our investigations show that in all cases so far 

 examined such variation in the type is the result of one cause 

 only, namely, natural cross-fertilization. If crossing is prevent- 

 ed and the various races are raised from self-fertilized seed, the 

 inheritance of all the characters down to the most minute shades 

 of difference is most marked. The observations and experiments 

 at Pusa point to natural cross-fertilization being the sole cause 

 of changes iii the race in the morphological sense. Soil, climate, 

 moisture and food materials, no doubt, influence the quality and 

 suitability of the leaf for various purposes, but we have not found 

 these causes lead to the breaking up of the type. 



Most observers agree that natural cross-fertilization occurs 

 in this species, but the extent to which it takes place when the 

 types are grown next to next does not appear to be fully realised. 

 The collection of Indian tobaccos made at Pusa in 1905 was 

 grown for two years on the Piisa farm, and a few plants of each 

 kind were allowed to flower freel}' in ] 906 and again in 1 907. 

 In 1907, we selected all the difl'eient types in this collection, and 

 saved the seed from each plant separately. The various sowings 

 were made by us in the Botanical area at Piisa the same year and 

 since that time all seeds used to propagate the cultures have been 

 selfed and raised under bag. Opportunities for natural crossing 

 were possible, therefore, at Piisa for two seasons only, and these 

 opportunities were limited b}^ the fact that but few plants of 

 each kind were allowed to flower and the period of flowering of 

 the various kinds did not in all cases overlap. In 1908, observ- 

 ations were made on the uniformity of the cultures raised from 

 one parent plant, and any individuals which varied from the rest 

 in the slightest degree were noted. In every case these aberrant 

 plants were selfed and grown the next year when the}'" gave rise 

 to a large number of forms, often very diverse in habit and in 

 leaves and which were obviously the products of natural cross- 

 fertilization (Plate I). In over a hundred cultures of this species 

 in 1908, about 20 per cent, of the rows contained aberrant plants, 



