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CHAPTER X. 
CLASSIFICATION OF FERNS. 
When first the study of ferns began to be lightly touched, 
the mode of classification was according to the shape of 
the frond. A very little further examination into the 
structure of the plants convinced the students that this 
mode of arrangement would not do. Then the form of the 
sori was fixed upon, and though good so far, alone it was 
not found to be sufficient. Sir J. E. Smith proposed the 
form and attachment of the involucre as the criterion of 
distinction in the family, and this mode of classification 
has given, and gives much clearness, and consequent 
satisfaction. Sir William Hooker follows this plan of 
arrangement, combining with it the observations noted 
by Mr. Moore and others, on the presence, modifica- 
tions, or absence of an elastic ring. The venation of the 
fronds and the connection of the veins with the sori are 
also points of immense importance in the investigation 
and classification of ferns. 
All ferns may be divided into Annulate and Exannu- 
late, the former division containing the true ferns, both 
dorsiferous , or bearing their fruit on the back of the 
frond, or marginal , bearing their fruit on the margin ; 
and the latter, including the pseudo-genera Osmunda , 
JBotrychium , and Ophioglossum . 
