136 STUDY OF COMMON PLANTS. 



widely distributed, and, in general, easily procurable. For 

 this part of tbe work, dried specimens are nearly or quite 

 as satisfactory as fresh ones. The comparison, while in- 

 cluding a study of external characters, should be directed 

 primarily to the fructification, which presents the really 

 distinctive features of the different genera. It is necessary 

 in each of the genera studied, to observe particularly the 

 form of the sorus and indusium, and the way in which the 

 latter is attached to the leaf. If ten or a dozen different 

 kinds of ferns are studied in this way, with accompanying 

 drawings and descriptions, the student will have learned 

 from his own observation the salient characters of the 

 ferns as a group, the marks that distinguish the more 

 prominent genera, and the features by which the species 

 belonging to them are recognized.^ 



The systematic literature is extended and rather expen- 

 sive. Eaton's Ferns of North America is the best for this 

 country, and the works of Hooker and Baker give the 

 most help on foreign species ; but with Gray's Manual or 

 Underwood's little book, the student will be able to iden- 

 tify without difficulty the ferns indigenous to the region 

 where he lives, and this is suggested to him as an interest- 

 ing and instructive piece of systematic work. 



1 For further hints see Underwood, Our Native Ferns and their Allies. 



