INTRODUCTION. 



391 



usually unbranched, erect or oblique stem of a somewhat tubercular form, bearing leaves 

 arranged close together in a spiral manner. The leaves are relatively large, are usually 

 much branched, and usually bear stipules at the base of their petioles. The sporangia 

 are borne either upon the under surface of ordinary leaves, or in spicate or paniculate 

 fructifications which are metamorphosed leaf-segments. They are derived from groups 

 of cells which form projections upon the surface of the leaves. The mother-cells of 

 the spores are found in large numbers. A single apical cell is present in the stem 

 and root. 



Families. (i) Ophioglosseae. 



(2) Marattiaceae. 



(3) Osmundaceae. 



(4) Schizaeaceae. 



Order II. Filices. The spores are of one kind and develope independent monoe- 

 cious prothallia. The second generation is either an erect unbranched stem, or a stem 

 which is more or less horizontal and bilaterally symmetrical and which branches occa- 

 sionally. The leaves do not possess stipules, are circinate in their vernation, and bear 

 upon their laminae, which may or may not be more or less specially modified, very 

 numerous sporangia usually arranged in sori covered by indusia. The sporangia arise 

 from distinct epidermal cells, and usually sixteen spore-mother-cells are formed in 

 each. The sporangia are opened by means of the so-called ring (annulus). Both 

 stem and root possess a single apical cell. The ground-tissue tends to become 

 converted into brown sclerenchyma, which especially supports the sheaths of the 

 fibro-vascular bundles. 



Families. (i) Gleicheniaceae (?), (Osmundaceae, Schizaeaceae?). 



(2) Hymenophyllaceae. 



(3) Cyatheaceae. 



(4) Polypodiaceae. 



Order III. RhizocarpesB. The sporangia are of two kinds, those of the one kind 

 containing macrospores, those of the other microspores. Within the macrospore a 

 small prothallium is formed which does not become separated from the spore ; within 

 the microspore the mother-cells of the antherozoids are formed from a very rudi- 

 mentary prothallium. The second generation is a bilaterally symmetrical, horizontal, 

 regularly branched stem, which bears leaves upon its dorsal surface in two or more 

 rows, and roots upon its ventral surface. {Sal'vinia is rootless.) The sporangia arise 

 from individual superficial cells of the placentae and are enclosed in sporocarps which 

 may be uni- or multilocular, and are formed by metamorphosed leaves or segments of 

 leaves. The placenta of each loculus of the sporocarp bears a sorus of sporangia, 

 and there are sixteen mother-cells of the spores in each sporangium. The microspores 

 are formed in great numbers in each microsporangium (4 x 16), but only one macrospore 

 in the macrosporangium comes to maturity. The stem grows by means of a two- or 

 a three-sided apical cell ; the root has always a three-sided apical cell. 



Families. (i) Salviniaceae. 

 (2) Marsiliaceae. 



CLASS IX. 



DiCHOTOMEiE. 



The prothallia are developed either from spores of one kind only and are then 

 independent and monoecious, or they are developed from spores of two kinds (macro- 

 and microspores), and then remain within the spore until the period of fertilisation. 



