546 PTERIDOPHYTA 



stems (Hydropterideae). The 1. are simple, except in many ferns. 

 There is no primary tap-root, but roots are formed as required from 

 the stem or 1. Internally there are well marked vascular bundles in 

 both stem and leaf, and many anatomical features of fig. pi. may be 

 found here also. 



The sporangia arise upon the 1., either on the ordinary foliage 

 as in most ferns, or on specially differentiated 1. as in Osmunda, 

 Equisetum, Lycopodiales Hydropteridineae, &c. They may be sol. 

 or in groups (son) ; in the latter case often protected by a special 

 outgrowth of the 1., the indusiinn. The spores are formed by a com- 

 plicated process from a single cell or row or layer of cells the 

 archesporium inside the sporangium : each has a thick waterproof 

 outside wall. The spores maybe of one kind only, in which case the 

 plant is termed homo- or iso-spomus, or of two kinds (heterosporous}, 

 when the smaller spore is termed the microspore, the larger the mega- 

 ox macro-spore ; the former gives rise to a cf prothallus, the latter to 

 a? . 



Falling upon the soil (or into the water, in the case of the 

 Hydropteridineae) the spores germinate under suitable conditions, 

 giving rise to the sevual plants or prothalli. The prothallus is a small 

 body without distinction into stem and 1. ; it absorbs materials from 

 the soil (usually by rhizoids) and, being green, assimilates in the 

 ordinary way. It bears the sexual organs antheridia ( 3 ) and 

 archegonia ( ? ) In the homosporous forms these are both found on 

 the same prothallus, except in Equisetum, where, though the spores 

 are absolutely similar so far as we can tell, there are separate 3 and 9 

 prothalli, as in the heterosporous forms. In the antheridia are 

 developed the motile 3 cells or spermatozoids. Pert, takes place by 

 aid of water. The mucilage contained in the neck of the archegonium 

 is attractive to the spermatozoids, which swim up the neck of the 

 archegonium. One of them finally fuses with the ovum or ? cell at the 

 base of the archegonium, and the fertilised ovum (zygote) then develops 

 into a new 'plant' or asexual generation, being nourished by the pro- 

 thallus until it can assimilate for itself. 



Classification (after Engler): 



I. Filicates. L. usu. more strongly developed than stem, often 

 big and much branched, usu. circinate in vernation. Spo- 

 rangia on normal or special 1., on edge or lower side, usu. 

 in sori. Spermatozoid polyciliate. 



1. Filicales Leptosporangiatae. 



2. Marattiales. 



3. Ophioglossales. 



[II. Sphenophyllales. Fossil plants only.] 



III. Equisetales. Homosporous (some fossils heterosporous), 



with dioec. prothalli. Stem much branched with jointed 

 internodes and small sheathing whorls of 1. (not green). 

 Sporangia on peltate sporangiophores, forming a term, 

 spike. Spermatozoids polyciliate. 



IV. Lycopodiales. Homosporous or heterosporous ; in the latter 



case the ? prothallus remains enclosed in the spore till fert. 

 Stem simple or branched ; 1. many, small, usu. alt., entire. 



