Resemblance between Plants of same District. 143 



It is not only the dying out of certain species that is 

 thus to be explained by changes in the external con- 

 ditions, and especially by changes in the animals to 

 whose attacks they are exposed, but the same considera- 

 tions account also for the further fact, that species of 

 plants, which, haviag regard to other characters, we 

 reckon as belonging to the most widely separated 

 families and races, nevertheless, if growing under like 

 external conditions, present similar peculiarities of 

 structure. Only such structural developments as are 

 of advantage are preserved, and only such individual 

 varieties as arise with characters adapted to the envir- 

 onment, can become the starting-points for new species. 

 As, however, the process of remodelling in adaptation 



ingredient in its blue flower ; for I gathered one year in Switzer- 

 land a hundred flower stems of this blue variety, and found not a. 

 single flower perforated ; whereas, on similarly examining a hundred 

 flower-stems of the white variety in the same district, I found 

 every open flower with a hole in the side. This probably explains 

 the much greater abundance of the blue variety. As regards 

 Shmavthm, I cannot but still think that the wide calyx is a con- 

 siderable protection against lateral pilfering of nectar. I have 

 examined a vast number of the flowers of Rhm. cristagalU, both in 

 England and in Italy, and very rarely indeed have I found the 

 coroUa perforated. Doubtless these exceptional instances are 

 enough to show that such perforation is not impossible. But there 

 was no necessity for nature to make it an impossibility. Her 

 object would be equally well attained if she made the lateral access 

 more difficult than the normal one by the mouth; for the bee 

 simply wishes to avoid trouble, and selects the easiest plan of 

 getting at the nectar. But it cannot, I take it, be questioned, 

 that the peculiar calyx of BJiiimnthus is a considerable, though 

 not absolutely insurmountable, impediment to the lateral perfora- 

 tion. — Editor.] 



