—7i— 



characters, and when two forms differed much in regard 

 to any one of them, I should be inclined to regard each 

 as a good species. There are other characters, however, 

 that are so variable as to be of little value in separating 

 species, and yet are of considerable secondary importance. 

 Among these I would name size, color, vestiture, texture, 

 and cutting of the frond. We may now give brief atten- 

 tion to these. 



Size. It is scarcely necessary to mention size in this 

 connection. It would be well to note, however, that size, 

 when acompanied by a difference in one or more of the 

 other non-essential characters, may indicate a sub-spe- 

 cies. Alone, it can produce only forms. Size, being due 

 principally to soil, moisture, warmth and light, an excess 

 or lack of these readily accounts for over-developed or 

 under-developed specimens. It is to be noted that some 

 of the elementary species of DeYries are chiefly charac- 

 terized by size. 



Color. Color plays a less important part in the iden- 

 tification of ferns than of flowering plants. Neverthe- 

 less, it often forms convenient distinguishing features of 

 minor importance. Shades of yellow-green usually indi- 

 cate shade plants that have been exposed to the sun, 

 while deep greens indicate plants from shady situations, 

 and gray-greens, plants that habitually grow in sun. The 

 decided blue-green hue of the marginal shield fern dis- 

 tinguishes it from all related forms, but it is certain that 

 if color alone was its only distinction, it would not be 

 considered a separate species. In the so-called OpJiio- 

 glossum arcnarium, we have an example of a form pro- 

 duced by exposure to sun and drouth. Due to these its 

 size is decreased, and its color is yellowed. Similar con- 

 ditions have doubtless served to produce the plants named 

 Ly co podium adprcssum and L. porophilum. As regards 

 Ophioglosswm, Hooker well says: "I confidently affirm 

 that were I to show the authors of many of the so-called 

 species of Ophioglossum preserved in the Hookerian 

 Herbarium their own specimens named by themselves, 

 and substitute Britain on the tickets for the distant coun- 



