HOWARD, HOWARD AND ABDUR RAHMAN. 309 



crossing actually does take place under these circumstances was 

 proved in a larger number of cases. 



Natural Cross-fertilization. 



During the year 1905 a collection of Indian tobaccos was 

 made by the Piisa Farm, and the sowings were made the same year. 

 A few plants of each sowing were allowed to run to seed without 

 being bagged, and this seed was again sown in the autumn of 1906. 

 In 1907, we selected seed from all the different plants that could 

 be found in these sowings, and the seed from each plant was sown 

 separately by us the same year. Opportunities for natural cross- 

 fertilization at Piisa were therefore possible for two seasons, 1906 

 and 1907, before we took over the work. As only a few of the 

 plants, however, were allowed to flower in both years, these op- 

 portunities were not numerous. Cross-fertilization, although 

 previously possible in the various tracts of India from which the 

 seed was collected, is not likely to be of frequent occurrence on 

 account of the fact that but few plants are allowed to run to 

 seed by the ryots and that the fields of N . rustica are very 

 scattered. In 1908, it was found that out of 45 rows of N. 

 rustica each grown from the seed of one plant, 9 were not uniform 

 but contained plants differing from the rest. In 1908, a largo 

 number of these aberrant plants were bagged as well as the parent 

 seed plants selected from the uniform rows. The seeds of these 

 plants were again sown separately the same year. In every case 

 the aberrant plants proved to be crosses and gave rise to the most 

 diverse forms (Plate V). In one case infertile plants, with 

 peculiar foliage which may possibly be hybrids between N. rus- 

 tica and N. tahacum were observed (Plate VI). The selected 

 plants from the uniform rows however bred true. Natural cross- 

 ing is therefore frequent in many types of this species, and it will 

 always be necessary in experimental work to obtain seed under 

 bag. 



In the Indian types of N. tahacum which have been studied 

 up to the present the anthers in the majority of cases burst just 

 as the bud unfolds. In some cases, however, pollination may take 



