NATURAL SCIENCES OP PHILADELPHIA. 235 



ON THE AGENCY OF INSECTS IN OBSTRUCTING EVOLUTION. 

 BY THOMAS MEEHAN. 



Since so much which has been learned in regard to the agency 

 of insects in the cross fertilization of flowers, I understand the 

 drift of scientific thought to be in the direction of the general 

 principle, that in the hypothesis of evolution insects play an im- 

 portant part. It does not seem to have occurred to any observer 

 that they may act as an obstruction to any great departure from 

 what we may take as the normal form that but for them varia- 

 tions would probably often be much greater than they are. 



It has fallen to my lot to observe and to place on record in the 

 Proceedings of the Academy of Natural Sciences of Philadelphia, 

 the American Naturalist, and elsewhere, that art has not so much 

 to do with garden variations as generally supposed ; that varia- 

 tions in nature are as great as in horticulture; and that the 

 florist's credit is chiefly due in preserving the form which un- 

 assisted nature provided for him. It was at one time part of the 

 essential idea of a species that it would reproduce itself. If any 

 variation occurred in nature, it was taken for granted that seed- 

 lings from this variation would revert to the parent form. But it 

 is now known that the most marked peculiarity in variation can 

 be reproduced in the progeny, if care be taken to provide against 

 fertilization by another form. Thus, the blood-leaved variety of the 

 English beech will produce blood-leaved beeches; and, as I have 

 myself found by experiment, the very pendulous weeping peach 

 produces from seed plants as fully characteristic as its parent ; 

 and when the double blossomed peaches bear fruit, as they some- 

 times do, I have it on the authority of a careful friend that the 

 progeny is doubled as its parent was. But I need not refer 

 particularly to this. Any intelligent florist of the present age 

 can testify to the fact, that varieties will reproduce themselves as 

 fully as the original forms from whence they sprung. 



I do not think botanists, as such, are so fully aware of these 

 facts as the florists are. They scarcely admit of much inherent 

 variation in form in nature ; but look rather to hybridization, and 

 insect agency in connection therewith, to account for the changes 

 when they occur. In order to avoid the possibility of these 

 agencies acting as the sole factors in evolution, I have generally 



