GROUP III. PTERIDOPHYTA : FILICIN^E. 355 



GAMETOPHYTE. The germination of the spores has not been observed, 

 but the mature prothallium has been described in the case of Ophioglosmm 

 pedunculosum and Botrychium Lunaria. In both cases it is tuberous, sub- 

 terranean, destitute of chlorophyll, monoecious ; the antheridia are sunk 

 in the tissue, and the short necks of the archegonia project but little. 

 It appears that the prothallium is saprophytic, though possibly it 

 may possess chlorophyll in the early stages of its development. In 

 Botrychium it is a somewhat ovoid body not more than half a line long, 

 with long scattered root-hairs, bearing the antheridia chiefly on its upper 

 surface, the archegonia chiefly on the lower. 



Ophioglossum vulgatum (the Adder's tongue) is the British species of this 

 genus; O. lusitanicum has, however, been found in Guernsey. The 

 epiphytic species are O. pendulum and 0. palmatum, both tropical forms ; 

 the latter has palmately-lobed sterile fronds. Botrychium is represented 

 in the British Flora by B. Lunaria (the Moon-wort) which occurs in hilly 

 districts. Helminthostachys includes the single, species H. zeylanica 

 which occurs in the Eastern tropics.- 



Order 2. Marattiaceae. This order includes the genera Marattia, 

 Angiopteris, Kaulfussia, and Danaea, none of which are European, but 

 are mainly tropical. 



SPOROPHYTE. In its general morphology the sporophyte agrees with 

 that of the Ophioglossaceae ; but the leaves are more numerous, much 

 larger, compound, and circinate in vernation, and each bears a pair of 

 stipules. Branching of the stem occurs only in Danaea; in Kaulfussia 

 the stem is a subterranean, creeping, dorsiventral rhizome. The roots are 

 somewhat fleshy, and are much branched. The apical growing-point of 

 both root and stem consists of a group of a few (four or more) initial cells. 

 The sporophylls are not differentiated into a sterile and a fertile portion, 

 but have the appearance of foliage-leaves. The numerous sporangia are 

 borne in sori on the ribs of the under surface of the sporophyll ; in 

 Angiopteris the sporangia of a sorus are free, whilst in all the other 

 genera they are coherent, forming a synangium (see p. 349). The spores are 

 numerous, and are either tetrahedral or radial. 



GAMETOPHYTE. On germination the spore gives rise to a dorsiveutral 

 green prothallium resembling that of the Leptosporangiate Ferns. 



B. HETEEOSPOROUS EUSPORANGIATJE. 



Order 3. Isoetaceae. This order includes the single genus Isoetes 

 which comprises about fifty species belonging to all parts of the globe. 

 Some of these are terrestrial (/. Duricei and Hystrix}, whilst others are 

 either altogether aquatic (e.g. I. lacustris, eckinospora, etc.), or amphibious 

 (e.g. I. velata, setacea, boryana). The British species are /. lacwtris, echino- 

 spora, and Hystrix. 



Isoetes has, of recent years, been generally included among the 

 Lycopodinse ; but it betrays a relationship to the Filicinae in so many 

 features, such as its general habit, its embryogeny, the absence of any 

 cone-like fructification, the form of its spermatozoids, that it appears to 

 be more natural to place the plant in that group. 



