PTERIDOPHYTA. 709 



The sporangium is sessile, and the annulus is situated at the apex like a cap (c/. fig. 

 400 1'*). In Schizcea (fig. 400 ') the fertile pinnules bear two rows of sporangia 

 partly sunk in little pockets; in the climbing fern Lygodium the leaflets bear little 

 fertile spikes at the margin, and the sporangia are sunk completely in little pockets, 

 one row on either side of the spike. In Aneimia the frond divides into two 

 portions— a green vegetative portion, and several fertile branches whose ultimate 

 ramifications are beset with naked sporangia. In habit Aneimia is not unlike a 

 Botrychium (cf. fig. 400 «). Of Schizseaceae there are some 70 species. 



Marattiacece. — Tropical Ferns, many of them attaining considerable dimensions. 

 The fronds are distinguished by possessing a pair of stipules at their base. The 

 sporangia are more bulky than in the families hitherto enumerated, and in Angio- 

 pteris are arranged in rows very close together, whilst in Marattia, Kaulfussia, &c., 

 all the sporangia of each sorus are joined together into little button or bean-like 

 bodies. There is no distinct annulus, though a little cap of cells possibly represents 

 one. There are 25 existing species, but this family was much more abundant, than 

 it now is, in palaeozoic times; their remains are abundant in the Coal Measures. 



Osmundaceat. — Here also the sporangium is destitute of annulus, and possesses 

 a Httle cap of cells in place of it. In Osmunda regalis, the Royal Fern, the upper 

 pinnules of the frond alone produce sporangia, but in such quantity that their whole 

 surface is covered with them; thus the tips stand out in marked contrast to the rest 

 of the frond (hence the name " Flowering Fern"). The other genus of the family, 

 Todea, resembles a Filmy Fern in the delicate texture of its leaves. There are only 

 11 species altogether. 



Ophioglossacece. — A small family including the Adder 's-tongue (Ophioglossum) 

 and Moonwort (Botrychium). The frond here divides into a sterile and a fertile 

 portion, the latter seeming to arise from the base of the former. In the Adder's- 

 tongue the sterile portion is unlobed, and the fertile portion spicate, the sporangia 

 being sunk in its substance. In the Moonwort (cf. fig. 400^) both parts are 

 branched, the fertile portion resembling a panicle. The prothallium in this family 

 is a Httle subterranean tuberous body. The origin from it of the sporophyte 

 generation has not followed in any instance. There are twelve species of Ophio- 

 glossacesB. 



Alliance XXIII. — Hydropterides, Rhizocarps. 



This alliance is nearly associated with the Filices and more particulai 'y with the 

 earlier rather than with the last-mentioned families of that alliance. All the genera 

 are more or less aquatic in habit; but their distinctive feature is the fact that they 

 are heterosporous, i.e. that some sporangia contain macrospores (one in each 

 sporangium) the others microspores. The sporangia are collected into sori, which 

 are inclosed by metamorphosed leaf -segments into little fruit-like bodies. 



Families: Salviniacece, Marsiliacece. 



All the members of the alliance agree in their aquatic habit and in being hetero- 

 sporous. The macrosporangia are larger than the microsporangia, and contain one 



