40 PALJEONTOLOGICAL BOTANY. 



have lost their characters by the maceration to which they 

 were subjected before fossilisation took place, ferns are more 

 durable, and retain their structure. It is rare, howeyer, to 

 find the stalk of the frond completely preserved down to its 

 base. It is also rare to find fructification present. In this 

 respect, fossil Ferns resemble Tree-ferns of the present day, 

 the fronds of which rarely exhibit fructification. Hooker 

 states that of two or three kinds of New Zealand Tree-fern, 

 not one specimen in a thousand bears a single fertile frond, 

 though all abound in barren ones. Only one surface of the fossil 

 Fern-frond is exposed, and that generally the least important 

 in a botanical point of view. Fructification is sometimes evi- 

 dently seen, as figured by Corda in Senftenbergia. In this case 

 the fructification is not unlike that of Aneimidictyon of the 

 present day. Carruthers has recently detected the separate 

 sporangia of Ferns full of spores in calcareous nodules in 

 coal (Plate I. Fig. 5). These have the elastic ring character- 

 istic of the Polypodiacea3, and in their size, form, and method 

 of attachment, they are allied to the group Hymenophylleas. 

 The absence of fructification presents a great obstacle to the 

 determination of fossil Ferns. Circinate vernation, so com- 

 mon in modem Ferns, is rarely seen in the fossil species, and 

 we do not in general meet with rhizomes. Characters taken 

 from the venation and forms of the fronds are not always to 

 be depended upon, if we are to judge from the Ferns of the 

 present day. There is a great similarity between the carboni- 

 ferous Ferns of Britain and America ; and the same species, 

 or closely allied species of the same genera as those found in 

 Britain have been met with in South Africa, South America, 

 and Australia. In the English coal-measures the species are 

 about 140. The PalaBozoic flora of the Arctic regions also 

 resembles that of the other quarters of the globe. Heer, in 

 his account of the fossil flora of Bear Island,* enumer- 

 ates the following plants : — Cardiopteris frondosa, C. poly- 



'^ Heer, Flora fossilis Arctica; Fossile Flora der Biiren Insel., 1871. 



