532 BOTANY 



The oldest known Pteridophytes are of Silurian age, a small num- 

 ber of Ferns being referable to these formations. In the Devonian 

 there were probably representatives of all the existing classes of 

 Pteridophytes, as well as forms which had no certain relation to 

 these. It is in the Carboniferous rocks, however, that there are found 

 the greatest number of these plants, which during this period played 

 a much more important part than they do at the present day, this 

 being especially true of the now relatively unimportant Lycopods 

 and Equisetales. 



Ferns. Recent studies have thrown much light upon the affinities 

 of the Palaeozoic Ferns. It seems pretty certain that these were for 

 the most part related to the Marattiacese, which at present are con- 

 fined to the Tropics and include but a small number of species belong- 

 ing to but five genera. The Marattiacese of the Carboniferous rocks 

 show very much greater variety than is found among their modern 

 descendants, some of which, like Danaea and Angiopteris, do not 

 seem to have altered much from their Palaeozoic ancestors. The other 

 living group of Eusporangiatae, the Ophioglossaceae, is scantily rep- 

 resented in a fossil state, although there is a good reason to assume 

 that it is an ancient type. 



The prevailing modern type of Ferns, the Leptosporangiatae, are 

 not certainly represented among Palaeozoic fossils, although there are 

 occasionally found annulate sporangia which seem to resemble those 

 of the lower members of the group, the Osinundaceae, Gleicheniaceee, 

 etc., and certain forms may have been synthetic types, combining 

 characteristics of the several families which become later completely 

 differentiated. One of these synthetic types has come down to the 

 present time in the genus Matonia, represented by two rare Ferns of 

 the Malayan region. Matonia is intermediate in character between 

 the Gleicheniaceae and Cyatheaceae, and is the sole living represen- 

 tative of a family which was abundantly represented in the Second- 

 ary formations by numerous species. During the Mesozoic age the 

 Marattiaceae of the Palaeozoic formations give way to the lower Lep- 

 tosporangiates, like the Osmundaceae and Gleicneniaceae, which in 

 the present flora are largely supplanted by the Polypodiaceae, now 

 comprising a very large majority of existing Pteridophytes. The 

 heterosporous Ferns, the Hydropterides (Marsilia, Salvinia) are only 

 scantily represented among fossils, and these all belong to the later 

 formations. 



Equisetales. The class Equisetales is at present represented by 

 about twenty-five species, all belonging to the genus Equisetum, the 

 last survivors of a once important and widespread group, some of 

 which were of tree-like proportions. The earliest remains of these 

 plants occur in the Devonian, and during the Carboniferous they 

 reached an extraordinary development. 



