84 THE STRUCTURE OF FLOWERS. 



CHAPTER IX. 



THE CAUSE OF UNIONS. 



Having now noticed the different kinds of unions, we may 

 ask what lias brought them about. 



We have seen how progressively complex conditions can 

 be traced from entire freedom, as in Buttercups, through 

 forms of Cohesion, such as the gamosepalous, gamopetalous, 

 monadelphous conditions, etc. ; to cases of Adhesion, as of the 

 perigynous and epipetalous states ; and, lastly, to the adhesion 

 of the ovary to the receptacular tube. 



As stated above, these conditions are correlated with 

 greater and progressive differentiations of the floral organs, 

 which have been brought about by insect agencies. The 

 above-mentioned and other terms do not, however, explain 

 how or what the immediate influences are which induce 

 unions of various kinds amongst the parts of flowers ; but 

 some researches of Mr. Meehan on the Coniferce * will perhaps 

 give us a clue. There is a well-known and a very generally 

 prevailing feature amongst certain genera of Conifers — as of 

 the CupressinecB, for example — that the foliage can appear 

 nnder two forms, the leaves being either free from theii' bases, 

 or more or less adherent to the axis. The two forms of leaves 

 have been recognized as specific characters in Juniperus, 



* On the Leaves of the ConifercB, Proc. of the American Association 

 for the Advancement of Science, 1869, p. 317. 



