226 Smooth-stemmed Form of Foxglove 



Summary of Conclusions. 



1. Digitalis purpurea occurs ^ under two distinct forms, the one 

 commonly accepted as the type with the stem grey and densely pubes- 

 cent throughout, and the leaves very hairy, here designated pubescens ; 

 the other, not apparently hitherto distinguished, with the stem green, 

 polished and smooth from the base to the flowering region where it 

 becomes pubescent, and leaves less hairy, designated nudicaulis. 



2. The two forms are similar in every respect except as regards 

 surface character. 



3. No difference in fertility was observed between the two forms 

 which set seed abundantly. 



4. The distinguishing feature of purpurea nudicaulis is a character 

 common to several other species within the genus. 



5. Both forms, when of pure parentage, breed true. 



6. Nudicaulis behaves as a Mendelian dominant when crossed 

 with pubescens and the erossbreds yield the monohybrid ratio 3 nudi- 

 caulis : 1 pubescens when self-fertilised and 1 nudicaulis : 1 pubescent 

 when crossed back with the recessive pubescens. 



7. The facts stated under 2, 3, 4, 5 and 6 do not support the idea 

 that nudicaulis is of hybrid origin. 



8. The alternative hypothesis of the origin of the one from the 

 other by direct mutation raises the question as to which represents the 

 original type, unless we postulate parallel development from a common 

 ancestor. 



9. In the absence of conclusive historical or geographical evidence 

 to the contrary, and in view of the fact that there is a certain difficulty 

 in supposing the origin of a dominant mutant form a recessive type, the 

 view that nudicaulis may be the earlier form and pubescens the derivative 

 seems at least worthy of consideration. 



10. The same argument may be advanced in the case of Linaria 

 alpina where also, according to the accepted view, we have in the recessive 

 spotted form the type and in the dominant concolor form the variety. 



