PTERIDOPHYTA. 15OI 



Class 2. Hepaticte. — The Liverworts differ from the Mosses 

 in the absence of true leaves, and in the bilateral condition of the 

 plant, which has the side exposed to the light differently organised 

 from the concealed one ; the oophore, moreover, generally arises 

 directly from the spore, the protonema, when present, being insig- 

 nificant. Hair-like growths, representing aborted leaves, are occa- 

 sionally present on the under side of the plant ; and it is fairly 

 certain that Liverworts are to be regarded as degraded forms which 

 have lost the leaves and branches of the Musci. The widely spread 

 existing genus Marchantia is represented in the European Eocene 

 and Miocene, and numerous Jungennanniacea have been found in 

 amber ; but beyond this nothing is known of the palaeontological 

 history of the class. 



Series II. Pteridophyta. — The Pteridophytes are characterised 

 by the great vegetative development of the sporophore, and the 

 tendency to the suppression of that of the oophore, or sexual 

 generation. Their tissue develops fibro-vascular bundles, and there 

 is a distinct epidermis. There is also a complete alternation of 

 generations, the spore developing a sexual prothallium (oophore), 

 from the archegonium, or female organ, of which is sexually pro- 

 duced the main plant or sporophore, which in its turn asexually 

 develops spores of one or two kinds in organs termed sporangia ; 

 the latter being generally borne either on ordinary or specialised 

 leaves, but in some cases on the stem. It will be apparent from 

 this that the main plant is an asexual sporophore corresponding 

 physiologically with the sporogonium of the Bryophytes, while the 

 sexual prothallium represents the leaf-bearing plant of the latter. 



The Pteridophytes — equivalent to the Acrogens of older writers — 

 are of extreme importance to the palaeontologist, since they contain 

 several groups of entirely extinct types ; and in the earlier epoch of 

 the earth's history, when they were not brought into extensive com- 

 petition with the Phanerogams, they attained an importance, both 

 in the number of types and in the large size attained by many of their 

 representatives, which entitles them to be considered the dominant 

 forms of the Palaeozoic epoch. 



Class I. Filicace^e. — The Ferns and their allies have the leaves 

 highly developed, and frequently much branched in a pinnate man- 

 ner ; the sporangia being numerous, and borne either upon the 

 ordinary or specially modified leaves, on which they are usually 

 arranged in groups or sort. The class may be divided into three 

 orders. 



The leaves of Filicaceae may be either simple, as in Glossopteris (fig. 

 1 376\ or pinnate. Among pinnate types the pinnation may be simple, 

 as in Nenropteridium (fig. 1373), when the leaflets or pinnules are ar- 

 ranged upon a single shaft ; or bi pinnate {Neuropteris, fig. 1371), when 



