50 THE PSILOPHYTON FLORA [en. 



But in many cases there is a strong family resemblance. Both 

 Arthrostigma and Thursophyton possess abundant emergences, 

 and also in habit are obviously not far removed from Psilophyton. 

 The former is also known to be vascular. The habit of Pseudo- 

 sporochnus (Figs. 15, 16, pp. 33, 34) is very remarkable and again 

 we are dealing with a vascular type. The bulb at the base of 

 the main axis (Fig. 15, p. 33) is an exceedingly algal feature, but 

 in the upper part of the plant the finer branches assume a more 

 or less Pteridophytic form (Fig. 16 b, p. 34), whereas the lower 

 axes (Fig. 16 a) resemble Thallophytes. Stur 1 originally regarded 

 this genus as an Alga pure and simple and even placed it in a 

 living genus (Sporochnus, Ag.) of that group, but Potonie and 

 Bernard 2 rightly point out that this genus is not a mere Alga, 

 as its vascular structure clearly shows. 



With regard to the other genera of the Psilophyton flora, 

 Ptilophyton 3 , Hostimella, Broggeria, etc., we make no remark in 

 this connection, save to point out that each is thalloid, and 

 appears to have some features in common with Psilophyton., and 

 that none of them are obvious Pteridophytes. They are however 

 still far too imperfectly known to afford any secure evidence of 

 the affinities of the flora to which they belong. Zoster ophyllum 

 is perhaps the most obscure of all, though as regards habit, it 

 may be compared with species of the living Alga, Nemalion. 



We shall discuss the bearing of the conclusions expressed here 

 in regard to Psilophyton in a later chapter (p. 70). 



In connection with the Psilophyton flora there remain one or 

 two matters which require consideration. It might be urged 

 that Psilophyton is a highly reduced type. The stomata are few 

 and it might be thought that it is a reduced xerophyte. Against 

 this view is to be set the clear anatomical evidence that the 

 lateral organs are emergences and not reduced leaves. It is very 

 unlikely that the latter would be microscopic, as we have seen 

 they frequently are in Psilophyton. The absence of any leaf 

 traces is again not what we should expect in the case of a leaf- 

 less xerophyte. But probably the most convincing argument of 



1 Stur (1881), p. 342. 2 Potonie and Bernard (1904). 



3 The terminal portion of this thallus is distinctly algal in appearance. 

 Cf. Procamium spp. 



