70 



CHAPTER VI 



THE PROCORMOPHYTA AND TH'E ORIGIN OF 

 THE CORMOPHYTA (EXTERNAL MORPHOLOGY) 



Historical. 



That these recent discoveries affecting the Psilophyton flora 

 have a very important theoretical bearing has been apparent to 

 all workers on the subject. Halle^ has recently entered into these 

 matters at some length and a further discussion is promised by 

 KidstonandLang^. The origin of Cormophyta is a problem which 

 has already attracted considerable attention, chiefly on the basis 

 of a study of recent plants. Bower's Origin of a Land Flora 

 (1908) contains an excellent epitome of these conclusions. In 

 addition there have been studies in which fossil plants of 

 Devonian age, and especially Psilophyton, have played some 

 part. The earliest of these was apparently Potonie's^ theory of 

 the descent of all Pteridophyta from Algal ancestors^, a view 

 which we are inclined to support enthusiastically. 



Potonie^ supplemented this conception by his pericaulome 

 theory, to which we shall refer again shortly. Both these 

 explanations appear to us to be on the right lines, although we 

 suggest a more limited application in regard to the pericaulome 

 theory than that which Potonie himself advocated. 



Almost simultaneously with Potonie's publications, a quite 

 independent series of conclusions were put forward by the late 

 Prof. Lignier. In 1903 Lignier^ postulated a primitive terrestrial 

 type, the Prohepatics, as having given rise to the Vascular 

 Cryptogams on the one hand and to Bryophyta on the other. 



1 Halle (1916), p. 35. ~ [See footnote, p. 48. A. A.] ^ Potonie (1898). 



* For a recent discussion of the same subject from the point of view of 

 a study of recent Algae see Fritsch (1916). [In this connexion see also 

 Church, A. H., Thalassiophyta, Oxford University Press, 1919 — a memoir 

 which had not appeared when the present book was written. A. A.] 



5 Potonie (1898), p. 19, (1902^) and (1902-). 



« Lionier (1903) and (1908). 



