76 ORIGIN OF CORMOPHYTA [ch. 



also figured from rocks as ancient as the Lower Ordovician 

 (Arenig) of the Lake District, similar specimens under the 

 name Protannularia {Buthotrephis) radiata, (Nich.). Examples of 

 these are in the Sedgwick Museum, Cambridge^. Nicholson^ 

 says " it is . . .difficult. . .to imagine what this can be if not a plant. . . . 

 It seems, however, pretty certain that if its vegetable nature be 

 conceded, it can hardly be referred to the Algae." With this . 

 conclusion we entirely agree, though we find no trace of any 

 vascular structure in the "leaves." It is quite possible that 

 Protannularia radiata may be the oldest, in a geological sense, 

 British land plant, and Procormophyte. Most authoritfes will 

 we think agree that these specimens have no real claim to a place 

 in the genus Annularia. We may transfer them to the non- 

 committal place of Protannularia. It may be objected that 

 these specimens are mere lusus naturae, mineral aggregates of 

 inorganic origin, but this does not appear to us to be the case, 

 so far as we have examined such fossils. 



We think it probable that the earlier examples may have 

 been simply Algae ^, while the later were Procormophytes — still 

 thalloid although vascular — and that it is conceivable that they 

 may have been among the ancestors of the Sphenopsida, though 

 as we haVe said they are at present still too obscure for any 

 weight to be laid on this suggestion. 



From some such ancestors as these, two lines of descent sprang 

 at slightly different periods, both inheriting a nodose arrange- 

 ment of microscopic branches. The branches became vascular 

 gradually, in exactly the same way as those of Psilophyton 

 became vascular. 



In the older line of descent, the Sphenophylls, the branches 

 were characteristically divided longitudinally into forked seg- 

 ments. This is well seen in the leaves of all members of this group 

 known in the Archaeopteris flora, i.e. SpJienophyllum (Fig. 24, 

 p. 52), Hyenia (Fig. 25, p. 53), and Pseudohornia (Fig. 26, p. 54). 

 These organs remain morphologically thalloid. The wedge-shaped 



1 The type No. 51 (also No. 1), Ordovician Plant Coll., Sedgwick Mus., 

 Cambridge. 2 Nicholson (1869), p. 497. 



' Such Algae still exist in the genus Crouania, etc., in which morpho- 

 logically though not structurally the habit is distinctly Sphenophyllaceous. 

 The living Lomentaria, Gaill. is in habit very equisetaceous. 



