VII.] CONCLUSION. 179 



conifers, &c., which are fertih'sed by the action of the 

 wind, did not therefore come within my subject. 



The causes which have led to the different forms 

 of leaves have been, so far as I Icnow, explained in 

 very few cases : those of the shapes and structure of 

 seeds are tolerably obvious in some species, but in 

 the majority they are still entirely unexplained ; and 

 even as regards the blossoms themselves, in spite of 

 the numerous and conscientious labours of so many 

 eminent naturalists, there is no single species as yet 

 thoroughly known to us. 



