1920] on The Earliest Known Land Flora 137 



of P. princeps. It was, however, the subject of adverse criticism by 

 his contemporaries, and the validity of the genus was questioned. 



It was upon a field so open as this that light has now been shed. 

 From fresh-water deposits of Lower Devonian age round Lake 

 Roragen, on the frontier between Norway and Sweden. Dr. Halle 

 collected many specimens of fossil plants. But they were mostly 

 impressions, and showed only imperfect preservation of their micro- 

 scopic structure. He distinguished several genera of plants with 

 branched cylindrical stems bearing small thorn-like appendages, and 

 some of them distal sporangia. Many of his specimens were referred 

 to Psilophyton princeps, and bore out in the main the reconstruction 

 of Dawson. Halle was able to confirm the existence of a central 

 vascular strand in Psilophyton, consisting of tracheides, a fact which 

 ranks it with certainty among vascular plants of the laud. But the 

 most distinctive novelty which Halle discovered in the Roragen beds 

 was a fossil which he called Sporogonites. It consisted of a simple 

 stalk bearing a terminal capsule. From its form, and the character 

 of its contents, he held it to be a sporogonium comparable with that 

 of the Bryophytes ; but a generalised type, not referable to any 

 existing group of them. An alternative suggestion was that Sporo- 

 gonites may represent only the upper part of a more highly developed 

 sporophyte, perhaps on the line of descent of the Pteridophytes. 

 Thus the presence of Sporogonites does not actually prove the exist- 

 ence of Bryophytes as we now know them in the Lower Devonian 

 Rocks. But nevertheless it has a peculiar interest. Hitherto there 

 has been no certain record of the existence of any moss-like type in 

 the Palaeozoic Period. The demonstration of so moss-like a 

 sporangium as Sporogonites is certainly the most thrilling of the facts 

 brought forward by Dr. Halle. 



In 1913, three years before Dr. Halle's publication of these dis- 

 coveries at Roragen, the first of the new observations of Lower 

 Devonian plants in Scotland was recorded. Dr. Mackie, of Elgin, 

 found at Rhynie, in Aberdeenshire, certain isolated blocks of chert 

 containing plant remains. A little later the source of these blocks 

 was traced to a bed of chert, of Old Red Sandstone age, found in situ 

 by the Scottish Geological Survey. Its origin appears to have been 

 this. An exposed land-surface existed there in Lower i >evonian 

 time, subject to intervals of inundation. It became periodically 

 covered by vegetation. By decay of its stems and underground 

 parts a bed of peat would be formed. The peat was then flooded, 

 and loose sand deposited over it. Again the vegetation was repeated. 

 and so successive bands were formed to some eight feet in thickness. 

 Then followed water with silica in solution, supplied from some 

 fumarole or geyser. The peat-bed was thus sealed up, and the 

 plants preserved with astonishing perfection. 



From this bed of chert four distinct vascular plants have been 

 recognised, and described in the minutest detail by Dr. Kidston and 



