192 KIDSTON: TlIK FLOKA OF TIIK CARBONIFEROUS PKHIOD. 



fructification, but before referring to these more fully it is 

 necessary very sliortly to ('onsidcr the fructification of existing 

 ferns. 



Recent ferns are divided into two great classes — the Iso- 

 sporous Ferns, or those with one kind of spore, and the 

 Heterosporous Ferns, or those with two kinds of spores — 

 macrospores and microspores. With the latter class, however, 

 we have nothing to do at present. 



Returning to the Isosporous Ferns, these again form two 

 great sections. Fii'st, those whose sporangia are provided with 

 a prominent ring of cells, called an Anntdus (Plate XXVIII., 

 fig. 2), and those whose sporangia are destitute of this structure. 



The first section contains the great majority of recent ferns, 

 of which the common Polypody and Male fern may be men- 

 tioned as well-known representatives. The second group con- 

 tains the Marattiacea', which comprises few genera and a small 

 number of species, all of which are natives of more or less 

 tropical areas. 



In Carboniferous times both these groups are represented, 

 though the exannulate ferns seem to have outnumbered those 

 with annulate sporangia. 



Let us now return to Sjyhenopteris. Many of the species 

 originally included in that genus have in recent years been 

 found showing their fi-uctification, and for these new genera 

 have been created. Among British Sphenopteroid forms a few 

 are known to possess annulate sporangia, and of such are 

 Corynepteris Baily and Oligocarpia Goppert. In the former the 

 sporangia are placed in groups of five or six, united at the base 

 around a common centre, and collectively form a globular mass 

 or sorus ; in the latter they form little circular heaps composed 

 of a number of independent sporangia. Isolated annulate 

 sporangia are frequent in the Yorkshire and Lancashire " Coal 

 Balls," and also occur in the material from Pettycur, Fife, which 

 is situated in the lowest division of the Carboniferous Formation 

 (Calciferous Sandstone Series). 



