— 7o- 



dots is sufficient to distinguish X cphrodium marginale 

 from N. Goldieanum. Dr. Christ recently united margi- 

 nale and Goldieanum as varieties of Nephrodium iilix-mas, 

 and the great amount of objection that instantly arose 

 proves to be founded upon a sound basis of fact. 



Shape of the Fruit-dots. When taken in connection 

 with the position of the fruit-dots upon the veins, the 

 shape of the fruit-dots offers another constant character. 

 It has always been relied upon in the separation of 

 genera, and doubtless always will be. The size of the 

 fruit-dots is scarcely less constant. There seems to be 

 no species with spore-cases in groups in which there is a 

 material difference in the size of the sori. This is so 

 well known that I have ventured to name a new form of 

 Cystopteris fragilis, which depends to a great extent 

 upon the presence of this single character. In species 

 with spore-cases in lines, it is to be expected that the 

 lines will vary somewhat in length, but in no other 

 particular. 



The Indusium. Prof. Underwood calls the indusium 

 the most variable and ephemeral of fern structures, and 

 says it is a mere flattened trichome more subject to vari- 

 ation than any other fern structure. This may be true 

 when the entire fern world is considered, but as regards 

 single species, the indusium is remarkably unvarying. 

 It is interesting to note, however, that the genus Pteri- 

 dium recently revived by Prof. Underwood depends 

 almost entirely on the presence of a second fugacious 

 indusium, to all intents in the nature of one of those 

 " mere flattened trichomes." 



Outline of the Froxd. This, also, within certain 

 limits, is of great importance in distinguishing species. 

 One must not be led too far by it, however. While the 

 general contour varies but little in any species, the cut- 

 ting of individual pinnae is exceedingly prone to vary, in 

 this following the rule of terminal parts generally. I 

 shall refer to this again in speaking of certain minor 

 characters. 



All the foregoing I am inclined to consider essential 



