312 NATURAL CROSS-FERTILIZATION IN INDIA. 



From the practical point of view the significance of natural 

 cross-fertilization in tobacco is very great. We have found at 

 Piisa that natural crossing is the only cause of the breaking up of 

 the type of any desirable kind of tobacco. If crossing is prevented 

 and the type is raised from self- fertilized seed, the uniformity of the 

 crop is extraordinary and no variability as regards the leaves or 

 in time of ripening occurs. Uniformity in the shape, size and tex- 

 ture of the leaves and in the time of ripening is of the greatest im- 

 portance in tobacco cultivation. Unless the crop ripens off uni 

 formly, the difficulties and expense of harvesting and curing are 

 increased. A crop made up of several types of plant differing in the 

 size, shape, venation, texture and thickness of the leaves does not 

 give a uniform product and unnecessary expense is involved in sort- 

 ing out the various grades for market. The production and mainte- 

 nance of the uniformity of the leaf is therefore a matter of the first 

 importance, and is, moreover, the first condition for the improve- 

 ment of the tobacco crop in India. This improvement can only 

 be maintained by the prevention of natural crossing and by raising 

 all seed under bag. Where a large number of varieties are grown 

 at an experimental farm, the greatest care will have to be taken to 

 keep the types pure and to prevent intercrossing. 



The introduction of exotic tobaccos into India and also the 

 testing of those from other localities in India itself are matters 

 intimately associated with natural crossing. It usually happens 

 that introduced seed is impure, giving rise to many types which in 

 some cases resemble each other sufficiently to appear to be homo- 

 geneous. No useful purpose is gained by distributing such seed to 

 cultivators. All the various types must first be sorted out, the 

 seed in each case being raised under bag. In this way all crossed 

 plants in the mixture can be eliminated and the best type or types 

 isolated and pure seed distributed. If introduced seed is given 

 to cultivators or used for experiments, it is not improbable that one 

 or more natural crosses or stray plants might be selected as seed 

 parents. In this way the type would be propagated from one or 

 more undesirable^^plants, and the quality of the kind quickly lost. 



