CH. Ill] 



PSILOPHYTON 



15 



chapter of this memoir to jiass in review the main facts relating 

 to the morphology and anatomy of these fossils. In each case 

 we begin with a summary of what appear to us to be the critical 

 features of each genus and we then 

 pass on to a discussion, also of a 

 critical nature, of the more recent 

 advances in our knowledge of each 

 type. 



It should, however, be clearly 

 understood that while some of the 

 genera here discussed are now placed 

 on a firm scientific footing, many 

 others remain extremely obscure, 

 and are as yet only of minor in- 

 terest. In the matter of the litera- 

 ture, we have contented ourselves 

 as a rule by quoting only the latest 

 of a series of memoirs dealing with 

 each subject. References to the 

 earlier literature will be found in the 

 papers quoted. 



PsiLOPHYTON (including Rhynia 

 and Dawsonites). 



(Figs. 1-7:) 



Psilophyton, Dawson, 1859. Ter- 

 restrial plants, consistingof a rhizome 

 from which dichotomously branched, 

 erect axes arise, the terminations 

 of which are circinately coiled in 

 the young state. Shoots leafless, 

 vascular, possessing stomata, and 

 emergences, the latter being either 

 macro- or microscopic. Fructifica- 

 tion consisting of sporangia borne ter- 

 minally on some of the erect shoots ; 

 wall of sporangium multi-layered. 



Fig. 1. Psilophyton. Dawson's 

 restoration of the sterile thal- 

 lus, published in 1859. This 

 restoration is correct except 

 in the matter of the lateral 

 organs borne on the longest 

 (central) axis. After Dawson 

 (1859). 



