170 STERILE AND FERTILE REGIONS 
distinction is very perfectly bridged over. But I submit that the most 
exact demonstration of similarity in detail of development, and the quotation 
Osmunda, L. A=O. Presltiana,\. Smallleaf. Band C=O. Regalis, L. B=young 
plant. C=leaf of a mature plant. (After Engler and Prantl.) 
of an infinity of middle-forms drawn from the most varied types of Ferns, 
does not touch the question of phylogenetic priority. Such facts are the 
