part 2] ANNIVERSARY ADDRESS OF THE PRESIDENT. ci 



type of vegetation became dominant, which not only marked a 

 striking advance in organization and in variety, but was no longer 

 hampered by the exigencies of swamp conditions. Trees with a 

 highly-differentiated mechanism, at least equal to that of recent 

 Conifers in the complexitj r of structure, were not uncommon; and 

 there is no reason to doubt their ability to respond to the demands 

 of relatively dry habitats. 



Our knowledge of Devonian vegetation in the Southern Hemi- 

 sphere is very imperfect. No undoubted examples of such charac- 

 teristic northern genera as Psilophyton and Thursophyton are 

 recorded, but too much weight may easily be given to this negative 

 evidence. It is not improbable that the older Devonian rocks of 

 the southern continents so far explored were formed under con- 

 ditions ill adapted to the preservation of peat-forming associations. 

 Reference has already been made elsewhere to the fairly frequent 

 occurrence in African deposits (some of which are either of Lower 

 or of Middle Devonian age, and others probably Upper Devonian) 

 of pieces of stems similar in external features to Protolepidoden- 

 dron, a Middle and Upper Devonian genus in North America and 

 Europe, to Gyclostigma, a characteristic Upper Devonian genus, 

 and exhibiting some resemblance to certain forms of the older 

 Arthrostigma. Attention should also be drawn to a specimen 

 figured by Dr. T. G. Halle from rocks in the Falkland Islands, 

 either Lower or Middle Devonian, as an indeterminable stem-frag- 

 ment : since the publication of Halle's paper the genus Hornea 

 has been discovered, and Halle himself has described a similar 

 type (Sporogonites exuberans) from Lower Devonian rocks in 

 Norway. A terminal globular swelling on the fragment from the 

 Falkland Islands shows a clear differentiation of a central region 

 and a more solid peripheral region, precisely as in the spore-capsules 

 of Hornea and Sporogonites. I may say that Dr. Halle agrees 

 with me that the resemblance is probably significant. Available 

 information does not warrant the assumption that the older 

 Devonian floras in the south were different in facies from those in 

 the north. 



In South Africa the Cape System includes a very considerable 

 thickness of sedimentary strata, largely unfossiliferous, and in part 

 (it is believed) formed under more or less arid conditions. Resting 

 upon the pile of almost completely barren sandstones of the Table 



