18G7.] Relations of Vcrbasca. 165 



chromatic' to those in which dissimilarly coloured varieties are united 

 In the following table we will at once see the comparative fertility 

 of these different unions given in the previous ones. 



Relative fertility of the Homochromatic and Heterochromatic 



Unions. 



1. V. phceniceum by its own pollen, . . . 1000 



2. V. phceniceum, rosea, by pollen of V. phceniceum, ... 958 



3. V. phceniceum, alba, by pollen of V^phamiceumj rosea, 867 



4. V. phceniceum, alia, by pollen of V. plucniceum, . ... 735 



5. V. phceniceum, by pollen of V. phceniceum, rosta, . ... 680 



6. V. phceniceum, by pollen of V. phceniceum, alba, ... 563 



7. V. lyclinitis, alba, by pollen of V. lychnitis, lutea } ... 822 



8. V. lychniits, lutea, by pollen of V. lyclinitis, alba, . ... 944 



9. V. blattaria, alba, by pollen of V. blattaria, lutea, .., 792 



10. V. blattaria, lutea, by pollen of V. blattaria, alba, ... 969 



11. V. thapsus, lutea, by pollen of V. thapsus, alba, . ... 947 



Here the comparative fertility is shown by calculation from 

 the number of seeds produced by 20 assumed capsules of both 

 unions. The various cross-unions of V. phceniceum and its varieties 

 are in each case to be considered relatively to the assumed results 

 of the pure unions of V. phceniceum given in Table 2, these 

 plants experimented upon being individually self-sterile as shown in 

 Table 1. The unions, on the other hand, of V. lyclinitis, blattaria, 

 and thapsus, with their respective varieties, are each to be considered 

 relatively to the 1000 seeds produced by the pure union of that 

 variety given as female. Now in all the above heterochromatic 

 unions, as compared with the homochromatic, we have the clearest 

 evidence of reduced fertility. Thus, taking the 10 heterochromatic 

 unions given, and comparing them with a similiar number of homo- 

 chromatic unions, we find that the average proportion in which the 

 former exceeds the latter, is as "05 to "23. On again confining 

 ourselves to those species alone which have the yellow and white 

 varieties, and keeping the unions of white as 2 with yellow $ , 

 distinct from those of yellow as p with white as $, we find that 

 the cross-unions with white as female are to the pure unions of the 

 latter as '04 to "28 ; and in those cross-unions with yellow as female, 



