INTRODUCTION. 33 



being the colour, shape and size of the corolla. As the investiga- 

 tion is complicated by the fact that species crosses were 

 employed with consequent sterility and as it is admittedly only 

 a preliminary account with very few data, it need not be further 

 considered here. 



A much more important paper dealing with N. tabacum only 

 was published by Hayes^ in 1912. The correlation and inheri- 

 tance of various characters such as the height of the plant, 

 number of leaves, average area of the leaves, average width and 

 average length of the leaves, were investigated in hybrids 

 between various pure types of American tobacco. Full details 

 are given of the measurements, but in no case have the cultures 

 been carried beyond the second generation. It was found 

 that the variability in the Fi generation and the parents was 

 similar but much greater in the Fo generation. These results 

 are most easily explained by the presence of a large number of 

 small factors with segregation. As regards the correlation 

 between these characters, the co-efficient in all cases was found 

 to be less than + . 5, except in the case of the length and width of 

 the leaf, where a distinct plus correlation was found. The 

 conclusions, as regards the individual characters, will be con- 

 sidered in more detail in the separate sections dealing with each 

 character in Chapter IV, but it may be remarked here that 

 although the results are undoubtedly valuable, many of the 

 measurements are taken in what appears to be a somewhat 

 arbitrary manner. For example, the number of leaves counted 

 is not the total number of leaves borne on the main stem of the 

 plant, but the number of leaves which occur between the fifth 

 leaf from the ground and the last leaf on a topped plant, this 

 representing the total number of leaves generally harvested. 

 Such numbers have an economic but no physiological meaning. 

 Similarly the height is measured to the last leaf counted, not 

 to the end of the main axis of the plant. As the habit of growth 

 of the American types used is very similar, discrepancies due 



^ Hayes, Bulletin 171, Connecticut Agricultural Experiment Station, 1912. 



