FLORAS OF THE PAST. 459 



evidence of the existence of algal species very similar in the 

 form of the thallus to certain recent seaweeds. We have on 

 the other hand some good examples of the genus Chara 

 which demonstrate the abundance of plants practically 

 identical with our modern freshwater stoneworts. 



Bryophyta. — Under this head there are no Wealden 

 species of special interest. Such fossils as may reasonably 

 be referred to this class have a close resemblance to Mar- 

 chantia as regards the vegetative form of the plant. 



Pteridophyta. — The two divisions of the Pteridophyta 

 most abundantly represented are the Ferns and Horsetails. 

 We will briefly consider the latter first and then pass on 

 to a few representatives of ferns. 



i. EqtiisetacecB. The numerous stem-casts ot various 

 species of Equisetites prove the abundance of slender 

 Horsetails in the Wealden vegetation. None of the stems 

 are much thicker than those of the larger species still 

 living in Europe, and so far as we know the fossil forms 

 agreed with their present-day descendants in the absence of 

 secondary wood. The Equisetums of the Lower Oolite, and 

 more especially those from Triassic rocks, had much thicker 

 stems, and very probably grew in thickness in a manner 

 comparable to the growth of the still older Calamites. The 

 rhizomes of some of the Wealden Equisetums bore branches 

 with tuberous internodes exactly like the oval tubers of 

 Equisetum arvense L., E. maximum Lam. and other species. 



2. FilicincB. Unfortunately many of the Wealden ferns 

 have as yet afforded little or no trustworthy evidence as to 

 their systematic position, and in many cases we cannot do 

 more than class the sterile fronds under provisional generic 

 names, or at best hazard a guess as to the family to which 

 they belong. There are however certain exceptions in 

 which the family characters have been satisfactorily deter- 

 mined. The literature on Jurassic and Lower Cretaceous 

 floras contains the names of several recent genera of 

 ferns which are supposed to be represented by fossil species, 

 but in not a few instances the choice of the name of a 

 recent genus has been made without any real evidence to 

 support it. Some of the most misleading determinations in 



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