THE VEGETABLE KINGDOM 339 



seems to have become a true seed, the microspores 

 germinating on it and fertilization taking place inside it. 



Filicales. The modern ferns are divided into three 

 groups, (i) Eufilicinae, which includes all the familiar 

 ferns : they are described as homosporous (producing one 

 kind of spores only) and leptosporangiate (the sporangia 

 developing from a single cell) ; (2) Hydropteridae, a small 

 group of water-ferns, which are leptosporangiate but 

 heterosporous (with mega- and micro - sporangia) ; 

 (3) Marattiales, a very small group which are euspor- 

 angiate (sporangia developed from a group of cells) and 

 homosporous. 



Fossil Eufilicinae, related to the recent Osmunda, are 

 known from Upper Permian upwards, and represen- 

 tatives of other families from the Upper Triassic 

 upwards. In the various estuarine beds of the Jurassic 

 of Yorkshire, for instance, there are found fern-leaves 

 closely similar to those of ferns now found only in the 

 Malayan region. Hydropteridae are known from the 

 Eocene upwards, but from earlier times the only records 

 are very doubtful. 



The Marattiales, however, are very well represented, 

 from the Carboniferous onwards. Some at least of the 

 species placed in the leaf-genus Pecopteris (Carb.-Jur.) 

 seem to belong to the tree-fern stem Psaronius (U. Carb.- 

 L. Perm.). Other forms are known from Mesozoic and 

 Cainozoic rocks. 



But the great majority of what have been called ferns 

 in the Carboniferous flora have proved to belong to a 

 higher grade. They may be related to the Marattiales 



