34 INTRODUCTION. 



to this method of measurement are not so great as they would 

 be in the case of many Indian tobaccos (see Plates I and II). 

 Nevertheless these arbitrarily chosen points cannot give the 

 expression of the true physiological activity of the plant as 

 regards height and number of leaves. 



A third paper on the inheritance of quantitative characters 

 in Nicotiana is that published b}^ Goodspeed.^ In the first part 

 of these investigations a comparison is made between the weight 

 of the seeds obtained by hybridization and the plants produced 

 from these seeds. N. tahacum var. macrophylla, a variety with 

 heavy seed, and N. tahacum var. virginica, a variety with light 

 seed, were employed as parents. The seeds of the Fj generation 

 were divided into three groups, heavy, light and medium, and it 

 is stated that in the plants raised from the heavy seeds the 

 greater number of individuals resembled var. macrophylla, 

 wliilein the culture raised from the light seeds the greater number 

 resembled var. virginica. The three classes of seeds showed 

 a difference in germinating power which was largely influenced 

 by time. The conclusion is therefore drawn that very variable 

 results may be obtained in the F2 generation which are due 

 merely to the differential germinating power of the various 

 heterozygotic and homozygotic combinations. The experi- 

 mental data on which these conclusions are based can, however, 

 only be regarded as most unsatisfactory. In the first place, 

 considering the number of characters and the probably infinitely 

 larger number of factors involved in the difference between two 

 varieties of tobacco, it would be practically impossible to divide 

 the Fo generation into three well-defined groups and any such 

 division which might be attempted would have no significance. 

 In tlie second place the original division of the hybrid seed 

 into three groups is open to question for the same reason. The 

 difference between these seeds probably depends on several 

 factors, and to these must be added environmental effects due to 

 mitriliou and pollination. Very little meaning can be attached 



^ Goodspoed, University of Galijornia, Pnhliratioui in Botany, Vol. V, No. 2, 1912. 



