RARE FORMS OF FERN WORTS -XVIII. 



The Forms of the Marginal Shield Fern. 



The marginal shield fern (Ncphr odium marginale) 

 is one of the most abundant and widely distributed 

 ferns in Eastern North America, and grows in a va- 

 riety of habitats besides the one which it prefers, but 

 with all its range of habitat, altitude, longtitude and 

 latitude it maintains' its form practically unchanged. 

 Many species of less promising appearance — such as 

 the polypody and harts-tongue — have far exceeded 

 it in the number of varieties produced in the wild, 

 while under cultivation a still greater diversity of form 

 occurs. As in practically all the ferns of the world, 

 forked fronds may be found if one searches long 

 enough, but even these are by no means as abundant 

 as in other well known species. 



The varieties of the marginal shield fern thus far 

 described have all clustered around the Cutting of the 

 pinnules, and may almost be set down to the vagaries 

 of luxuriant growth processes. We see anologous 

 cases in the leaves or vigorous young twigs of many 

 flowering plants, where there is a tendency to a deeper 

 cutting of the margins. Ordinarily the fern is pin- 

 nate with pinnae that are pinnatifid in the upper por- 

 tion and inclined to be pinnate below. The pinnules, 

 themselves, are usually short and blunt-ended with a 

 wavy margin that faintly indicates the point of de- 

 parture of the varieties. This is the form illustrated 

 in Eaton's "Ferns of North America" and is illus- 

 trated herewith at 1. As we have indicated, the de- 

 scribed varieties are all mere stages in more luxur- 

 iant and deeply cut specimens. When the wavy mar- 

 gins give place to decided ear-like segments, the 

 writer's form HpinnatiUdum results. A pinna is illus- 

 trated at 2. The variety clcgans, of Robinson is so 



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