230 A GENERAL REVIEW OF THE SIMPLICES [ch. 



cambial thickening may occur. The leaf-trace in HelviintJiostachys and 

 BotrycJiiuvi is always undivided, but the disintegrated stele in Cheiroglossa, 

 and the divided leaf-trace in OpJiiodernia are features shared only with rela- 

 tively advanced Ferns: moreover the reticulate venation of the whole genus 

 Ophioglossum is itself a Mesozoic feature : it is not shared by Helminthostachys 

 or Botiychmm, nor by any of the Coenopteridaceae, all of whose fronds are 

 of the open, Palaeozoic type of venation. Thus Ophioglossiun shows definite 

 signs of advance. The large sporangia in some Ophioglossaceae compare 

 readily with those of certain Coenopterids, especially where, as in BotjycJihim 

 and Helminthostachys, a vascular strand runs to the base of each, as it does 

 also in Stauropteris. The opening mechanisms are simple. The spore-out- 

 put is large : in OpJiioglossiim it is probably the largest in any Pteridophyte. 

 But the mere numerical total of spores cannot be held to prove that genus 

 to be the most primitive of all, as against the relatively advanced features 

 of its vascular system. The sexual organs and the embryology in the 

 Ophioglossaceae have been seen to be comparable to those of other living 

 EuSporangiate Ferns. The sum of these characters justifies the general 

 position here assigned to them, but with a special relation to the Coenop- 

 teridaceae. 



The Marattiaceae bear typical Eusporangiate sporangia, disposed in sori 

 of a primitive type, often synangial, and borne on leaves which are also 

 primitive in many features, having as a rule open dichotomous venation and 

 bearing dermal hairs: scales are present only in the synangial CJiristensenia 

 and Danaea, which may be held as advanced on both of these grounds. 

 Anatomically all the Marattiaceae are relatively advanced. Their sappy 

 stems and leaf-stalks contain a vascular system in a high state of disintegra- 

 tion, which finds a feeble analogy in the sappy stem of Ophioglossum pal- 

 matum. But it is prefigured by the Psaronioid stems of the Permian Period, 

 which have been held as related to the Marattiaceae. It seems uncertain 

 whether these, and certain Fern-like fronds from the Upper Palaeozoic 

 floras bearing sori of Marattiaceous type, should be included in the Family 

 as at present defined. Seward states (Hooker Lecture, p. 235, 1922) that 

 the oldest examples of fronds with fertile pinnae agreeing generally in habit 

 with modern Marattiaceae are from the Upper Triassic beds, while the 

 maximum development of the Family as we now know it seems to have 

 been in pre-Cretaceous times. It is clearly an ancient stock still surviving. 

 The characters of the gametophyte, sexual organs, and embryology accord 

 with this conclusion. 



The Osmundaceae which date from the Permian Period are, of all the 

 early Ferns, to be held as most nearly representing a central stock from 

 which many Leptosporangiate Ferns may have taken their origin. They 

 have long been recognised as occupying a position intermediate between 



