PTERIDOPHYTA 273 



The lower members of tlie series, however, especially the Osmun- 

 daceae, are to some extent intermediate in this respect between the 

 Eusporangiates and the more specialized Leptosporangiates. 



The Leptosporangiatae may be divided into two orders, the Filices, 

 or homosporous forms, and the Hydropteridineae, or heterosporous 

 Ferns. The latter develop two sorts of spores, large ones (Macro- 

 spores, Megaspores) and small ones (Microspores). The megaspore 

 gives rise to a female gametophyte, the microspore to the extremely 

 reduced male plant. 



Order I. Filices 



The general characters of the Filices have already been given in 

 the earlier part of the present chapter. The gametophyte is always 

 relatively large, and usually bears both archegonia and antheridia. 

 The sporophyte ranges from a centimetre or less in height (Tricho- 

 manes parvulum) to ten or fifteen metres (Cyathea sp.~). They are 

 for the most part moisture-loving plants, and are sometimes genuine 

 aquatics (Ceratopteris thalictroides). Some e.g. Gymnogramme tri- 

 angularis are more or less marked xerophytes. In the Tropics many 

 species, especially among the Hymenophyllacese and Polypodiaceae, 

 are epiphytes. Some of these epiphytic Ferns, like Platycerium, 

 produce special sterile, closely overlapping leaves, which serve to 

 hold moisture, and to accumulate decaying vegetable matter and 

 dust which are utilized as sources of food. 



Sporangium. The sporangia in the homosporous Ferns are always 

 borne upon the backs of sporophylls, which are usually not much 

 modified, although sometimes e.g. Onoclea, Struthiopteris, Blechnum 

 spicant, etc. the fertile and barren fronds are decidedly different. 

 In other Ferns, like Lygodium and Aneimia, special fertile leaf-seg- 

 ments are developed. The sporangium in all cases develops a single 

 tetrahedral archesporial cell, and the ripe sporangium has its wall 

 composed of but a single layer of cells. An annulus is always 

 present, and the form and position of the annulus are the most im- 

 portant characters employed in dividing the Filices into families. 



Classification. The Filices may be divided into the following 

 families: 1. Osmundaceae ; 2. Gleicheniacese ; 3. Matoniaceae ; 

 4. Schizaeaceae ; 5. Hymenophyllaceae ; 6. Cyatheaceae; 7. Parkeri- 

 aceae; 8. Polypodiaceae. 



Family i. Osmundaceae 



The Osmundacese are the lowest of the Leptosporangiates, and in the charac- 

 ters of both gametophyte and sporophyte are to some extent intermediate 

 between the typical Leptosporangiatae and the generalized Eusporangiates. The 

 gametophyte is large and not unlike that of the Marattiaceae. The character of 

 T 



