VIII. 



EQUISETACEAE, MARSILIOIDEAE, TRAQUAIRIA, 

 SPOROCARPON. 



THERE is nothing more indicative of the revolution, which has been 

 accomplished in the domain of palaeophytology during the last twenty or 

 thirty years, than the fact that the Equisetaceae, which were formerly con- 

 sidered to be the best-known of all fossil vegetable remains, are now one of 

 the groups with which we are not so well acquainted. The reason is that, 

 except in the case of Calamariae whose connection with Equisetaceae is 

 doubtful, we have no remains of this family before us in the form of 

 petrifactions showing structure, but are limited entirely to casts and im- 

 pressions. The smaller leafy branches and fructifications, the latter very 

 few in number, are known only in the form of impressions ; the main stems, 

 which are sometimes of great size, are usually found as casts ; and these 

 may be either casts of the broad cylinder of pith surrounded by a rind of 

 coal, or may represent the outer surface of the stem itself. Consequently it 

 is from the habit chiefly that the remains are determined ; we conclude that 

 they are Equisetaceae from the sheaths with their toothed margins, from 

 the big interior casts which point, as was said, to a broad cylinder of pith, 

 from the striated surface, and from the remains of fructifications which may 

 happen to be found with them. But most of these determinations in the 

 absence of any knowledge of the anatomy are to a certain extent insecure ; 

 and this insecurity is the greater, because we are acquainted with a series of 

 forms having exactly the same habit, the Calamariae, in which the structure 

 is in many respects essentially different from that of our living Equisetae, 

 and because we do not know whether the forms supposed to be Equisetaceae 

 agreed in this respect more with the one or with the other group. The 

 latter difficulty meets us of course chiefly when dealing with the remains of 

 the Palaeozoic and Mesozoic deposits ; doubts and considerations of the kind 

 are less important in the case of the many described Equisetitae from the 

 Tertiary formations which will be found collected together in Schimper l . 

 The period of the greatest development of Equisetaceae appears to have been 



1 Schimper (1), vol. i, p. 259. 



