SKOT. 1 CRYPTOGAMS 447 



Order 1. Equisetaceae. — Horse-tails. Homosporous. 



3. Li/copodinae. — Club Mosses. Stems elongated, dichotomously 

 branched, either forked or forming a sympodium, with leaves, in 

 many cases greatly reduced, or submerged, shortened, and tuberous 

 with awl-shaped leaves. Sporangia arising singly in the form of 

 fii'm-walled capsides either from the stem in the leaf-axils, or from 

 the leaf -base. Tapetal cells persistent. 



Order 1. Lycopodiacme. — Club Mosses. Homosjjorous. 

 Order 2. Selaginellaceae. — Heterosporous. 

 Order 3. Isoefaceac. — Heterosporous. 



There are also various fossil groups, some of which are included 

 in the above divisions, while some form independent classes. 



Class I 



Filicinae (Ferns) (i-*) 



The great majority of existing Pteridophytes belong to the 

 Ferns, taking the group in a wide sense. Two sub-classes are 

 distinguished according to the structure of the sporangia. The 

 Eusporangiate Ferns are characterised by sporangia, the thick wall 

 of which consists of a number of layers of cells. They open by a 

 transverse split. The Leptosporangiate Ferns on the other hand 

 have sporangia which when mature have their wall formed of one 

 layer of cells. Stipules, which are found at the base of the frond in 

 the former group, are wanting in the Leptosporangiatae. Differences 

 also exist in the prothallus and in the structure of the sexual organs. 



^Vhile in earlier geological periods the Eusporangiatae were abundantly 

 rejiresented, tliey now include only two families, each with a few genera. They 

 appear to represent the more ancient type of Ferns and to stand nearest to the 

 forms from wliich both Filicinae and Lycopodinae have been derived. Along with 

 them even in palaeozoic times we have the Leptosporangiatae, from which the 

 Hydropterideae have branched off as a small group of aquatic or marsh-growing 

 Ferns. In the Hydropterideae only among Ferns the spores are differentiated into 

 microspores and macrospores. 



Sub-Class I. Eusporang^iatae 



Order 1. Ophioglossaceae ('-^) 



European exami)les of this order are afforded by Opliioglossum vulgatum, 

 Adder's Tongue (Fig. 39"2, B) and Botrycldum, Moonwort (Fig. ^92, A). Both have 

 a short stem, from which only a single leaf unfolds each year. The leaves in both 

 cases are provided with leaf-sheatl s. In OjMoglossum the leaf is tongue-shaped, 

 in Botriichium it is pinnate. These leaves bear on their ujiper side a fertile 



