CABKIKl.I.K I,. C. flOWAIM). 



the laro-or imtiilxT of leaves. 'I'lie litiiits of the F., freiieratioii 

 are as great as those of the ))arents coinhined. !)iit no ui-eatei'. 

 The eiirve ohtaincd from its graj)lii(' rcpresctitatioii (Plate XIV) 

 points to distinet segregation, as do also t he icsults ()l)taiiie(l from 

 the F;, eiiltTiT'(>s. 'I'he following cultures a])j)ear to be miifoiiii, 

 Xos. 251 and liHi. with an average number of t liiit\- leaNcspcr 

 plant, and 2(»2. A\ith an average of twenty-six. This is another 

 instance of the pioduct ion of a plant possessing a nu mber of leaves 

 intermediate l)etween those of the pai'ents and breeding tiue. 



Table X gives the results in the cross Type 23 : Type 38, 

 which are very similar to those in Table IX. The Fi genei'ation 

 again approaches the parent with the greatest numbei- of leaves. 

 Distinct segregation occurs in the F:,, but no cultures bieecUng 

 true were found. 



As regards the ])rinciples underlying the inheritance of the 

 number of leaves per plant, there seems no (hjubt that this 

 is a definite inherita])le character, and that on hybiidization 

 segregation occurs with the formation of new homozygotic 

 combinations. In deahng with the mode of inheritance we are 

 confronted with the same difficulty as in the case of the height, 

 namely, the im]^ossibility of a plant ^^itllout leaves. Hayes 

 supposes a basal condition of x leaves which occurs in all tobacco 

 plants with a number of small interchangeable factors, each of 

 which may ie]:n'esent two leaves. Thus the same number of 

 leaves per plant may in regality have been caused by diffV^'cnt 

 combinations of charactei's, i.e., twenty-two leaves may be 

 X + AAbb or x -t BBaa. 



There is nothing in the results obtained in these investi- 

 gations to contradict this hypothesis of a basal number of leaves 

 combined with interchangeable factors. The results in the 

 cross Type 9 x Type 51 appear to be a direct confirmation. Ibit 

 the form of the curves obtained in the F. genei-ations i)oint 

 distinctly to the occurrence of factors of different values. If all 

 the factors were more or less ecpial in value the form of the curve 

 would be more imiform. and would iu)t show such distinct modes. 



