CRYPTOGAMS 443 



CLASS I. 



Filicinae. Ferns ( 108 ) 



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 ; the sporangium 

 originates from a group of epidermal cells together with the cells 

 lying just below the epidermis. The Leptosporangiate Ferns on the 

 other hand have sporangia which when mature have their wall 

 formed of one layer of cells ; each sporangium arises from a single 

 epidermal cell. Stipules, which are found at the base of the frond 

 in the former group, are wanting in the Leptosporangiatae. Differ- 

 ences also exist in the prothallus and in the structure of the sexual 

 organs. 



While in earlier geological periods the Eusporangiatae were abundantly 

 represented, they 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 which both Filicinae and Lycopodinae have been derived. The 

 Leptosporangiatae, from which the Hydropterideae have branched off as a small 

 group of aquatic or marsh-growing Ferns, may be derived from the Eusporangiatae. 

 In the Hydropterideae only among Ferns the spores are differentiated into micro- 

 spores and macrospores. 



Sub-Class I. Eusporangiatae. 



Order 1. Ophioglossaceae ( 109 ). 



This family may be placed first since it appears to contain the existing forms 

 which stand nearest to the primitive ferns. European examples are afforded by 

 Opltiocjlossum vulgatum, Adder's Tongue (Fig. 403 B) and Botrychium, Moonwort 

 (Fig. 403 A}. Both have a short stem, from which only a single leaf unfolds 

 each year. The leaves in both cases are provided with leaf-sheaths, and peculiarly 

 divided into fertile and sterile segments. In Ophioglossum the sterile leaf-like 

 segment is tongue-shaped, the fertile segment narrow and cylindrical, bearing 

 the sporangia in two rows sunk in the tissue. The sterile portion of the leaf 

 of Botrychium is pinnate, while the fertile segment is pinnately branched, and 

 thickly beset on the inner side with large nearly spherical sporangia. 



Our knowledge of the peculiar monoecious prothalli of the Ophioglossaceae is 

 largely due to BRUCHMANN ; they are long - lived, subterranean, sapropliytic, 

 tuberous bodies without chlorophyll but inhabited by a mycorhizal fungus. In 

 Ophioglossum (Fig. 403 C) they are cylindrical and radially symmetrical, simple 

 or branched ; in Botrychium they are oval or heart-shaped and dorsiventral. 

 The antheridia (Fig. 404) and archegonia (Fig. 405) are sunk in the tissue of 



