THE PllINCIPLE OF COHESION. 



51 



-Mimnlus undergoing "Dialysis' 

 (after Baillon). 



aided by the close proximity of the parts; and as a resulting 



effect, is the ever-increasing adaptation to the requirements 



of insects, which are more and 



more specialized for them, so 



that, for example, Lepldoptera 



are almost solely adapted to 



long tubular flowers like the 



Honeysuckle. 



An analogous process of 

 congenital cohesion is well seen 

 in the fasciation of stems which 

 occurs particularly often in 

 succulent shoots, as Asparagus, Cabbage, Lettuce, and the 

 young shoots of the Ash tree. This is most reasonably 

 referred to hypertrophy coupled with the close proximity 

 of the buds which ought to have developed into independent 

 shoots. Again, cohesion between the sepals or petals of 

 Orchids is not uncommon abnormally under cultivation ; and 

 would also seem to be due to the stimulating conditions under 

 which they are artificially cultivated. 



Hypertrophy in an organ is due to a special flow of 

 nutriment to it ; and cohesion may result from the close 

 proximity of the parts of the whorl to one another ; but the 

 influence which brin<^s about the determination of sap to a 

 particular point, I take to be the mechanical strains induced 

 by the insect visitors when alighting upon the flower iu 

 search for nectar or pollen. 



If this principle be correct, that the tubular structure of 

 calyces and corollas, as we see them now, has arisen through 

 the requirements of those organs to meet strains thrown upon 

 them ; I think it will furnish the solution to many a question 

 that may arise as to the peculiar shapes of corollas, etc., 

 besides expliaining the very principle of cohesion itself. An 



