cuAP. IV.] FILICES. 461 



SUB-CLASS 1. FOLIACEiE. 

 ORDER CCXL— FILICES.— THE FERN TRIBE. 



Though some of the Ferns are so common 

 that almost every one must have seen them, 

 very few persons are aware how very curiously 

 they are constructed. In the first place, they 

 may be said to have neither stems nor leaves, 

 and neither flowers nor seeds. The different 

 parts of the plant spring from a rhizoma, and 

 the leaves, which are called fronds, have their 

 veins neither branched nor in parallel lines, but 

 forked. On the back of the leaves are some 

 curious brown spots of various shapes called 

 sori ; and these, which generally form under the 

 outer skin or cuticle of the leaf, and which 

 always spring from one of the veins, contain a 

 number of small grains, called the thecse, which 

 are in reality cases containing the sporules or 

 seeds. When the sorus forms under the cuticle 

 of the leaf, the membranous part raised, which 

 resembles a blister, is called the indusium ; but 

 sometimes the sori are naked, that is, they are 

 formed on the outside of the cuticle ; and some- 

 times they are found on the margin of the leaf, 

 which folds over them, and supplies the place of 

 the indusium. The order is generally divided 

 into two sections, called Polypodiacese and 

 Osmund acese. The first contains those plants 



