PTEEI DOPHYTA— FILICIN^ 127 



Class YI.— FILICIN^. 



The usual classification of the forms included in this class is 

 as under : — 



Sub -Class IsospoRE^. — One kind of spore onlj- is produced ; 

 on germmation it gives rise to a free pro- 

 thallium. 

 Section 1. LeptosporangiatcB. — Each sporangium is pro- 

 duced from a single epidermal cell. 



This section includes most of the Ferns 

 proper. 

 Section 2. Eusporangiatce. — Each sporangium arises 

 from a group of epidermal cells. 



This section includes the Ophioglos- 

 saceae and Marattiaceae. 

 Sub-Class Heterospore^. — The spores are of two kinds, 

 microspores and macrospores or megaspores. 

 The prothallia do not become free from the 

 spores on germination. The microspore produces 

 a prothallium bearing an antheridium, the 

 macrospore develops one bearing archegonia. 

 Neither form of prothallium is ever free from 

 the spore. 

 Section 1. Leptosporangiatce. — Each sporangium arises 

 from a single epidermal cell. 



This section includes the water ferns, 

 Hydropteridese, sometimes called the Rhizo- 

 carps. 

 Some botanists place a second section here to include the 

 Isoetacese, which are eusporangiate. They are, however, gene- 

 rally included among the Lycopodinae. 



Section 1. — Isosporous Leptosporangiate Ferns. 



The sporophyte of this group is the plant usually termed a 

 Fern. It has generally a conspicuous body, morphologically 

 differentiated into stem, roots, and leaves. 



The stem is usually a creeping underground rhizome, though 

 in some cases it is borne upon the surface of a tree, and in 

 others, as in the tree ferns, it grows vertically into the air. It 

 usually gives off a number of adventitious roots and bears a 



