76 d FILICALES. [Acroge.xs. 



the importance of the fructification of Fems, as affording distinguishing characteristics 

 of generic groups, the modifications of venation might with convenience and propriety- 

 be admitted to share the same office ; and, according to this view, if two wild species 

 presenting constant organic differences in fructification, should not be placed in the 

 same genus, so neither should species presenting constant organic differences in the 

 development of their vascular structure. The question " whether or not a reticulated 

 venation is in itself a sufficient generic distinction among the Ferns," was answered 

 by Mr. Moore in the affirmative, on the ground that, a genus being an arbitrary group, 

 all that is required in a generic character is a constant difference from established 

 genera in the structure or development of some important organ. The vascular 

 system of plants is held to be of the highest importance in the vegetable economy, 

 since it is not unfrequent — and more common among Ferns than most other plants 

 -to find such extraordinary means of propagation as adventitious buds, developed in 

 connection with it. In Ferns, particularly those points of the veins which normally 

 serve as the receptacles which bear the sort, in other cases become viviparous and 

 devclope gemmje from which plants are ultimately produced. On these grounds 

 and the peculiarities of venation exhibited by flowering plants, the author arrived, 

 though with much deference, at a conclusion opposed to that of the botanists who 

 exclude venation in Ferns from the sources available for generic distinction. 



