K.— BOTANY. 211 



Schuclieit's contribution will stimulate South African geologists to 

 obtain additional evidence which will bring us a stage nearer to an 

 agreement upon this much-debated question. Meanwhile I am not 

 shaken in my opinion that if we could transport ourselves back through 

 the ages into a forest of the northern hemisphere in the latter part of the 

 Upper Carboniferous period, and thence travel by aeroplane to the land 

 that is now South Africa we should find retreating glaciers and a vegetation 

 in which Glossopteris and Gangamopteris were prominent plants. 



A Critical Stage in the History of the Plant World. 



There is another exceptionally interesting problem on which more 

 light is urgently needed, a problem too formidable to consider in the latter 

 half of an address, but attractive enough to mention as a subject worthy 

 of attention on the part of South African investigations. It is this : the 

 closing stages of the Palaeozoic era in the northern hemisphere were 

 marked by widespread crustal displacements ; a geological revolution 

 brought into being chains of Palseozoic Alps ; the scenes were shifted ; 

 the forests of the Coal period were replaced by a less luxuriant vegetation 

 growing under a new set of climatic conditions. Crustal movements are a 

 determining factor in the evolution of the plant kingdom : in other words, 

 geological revolutions afford an impressive example of the co-ordination of 

 the inorganic and organic worlds, a theme which has been elaborated by 

 General Smuts in his fascinating book ' Holism and Evolution.' The 

 vegetation of the early part of the Permian period, though generally 

 similar to that of the latest stage of the Carboniferous period, was relatively 

 much poorer in genera and species. The later Permian Floras were still 

 poorer, and the records of the early days of the Triassic period point to the 

 further development of the arid conditions foreshadowed before the end of 

 the Permian age. Later in the Triassic period the vegetation became 

 richer as the environment improved, but it was a transformed vegetation 

 in comparison with the forests of the Coal Age, a much more modern 

 company dominated by a different set of plant communities. There were 

 connecting links between the Palaeozoic and the early Mesozoic Floras, 

 but in the main the two floras differed widely from one another. The more 

 orderly succession of plant-bearing strata in most parts of the southern 

 hemisphere justifies the hope that an intensive and comparative study of the 

 transitional stage between the earliest and the latest phase of the Glossop- 

 teris Flora will furnish valuable data. In this field of work Mr. Du Toit 

 has shown the way : may his example be followed. The fragmentary 

 documents scattered through the rocks at the boundary between the two 

 eras relate to a critical stage in the fortunes of the plant-world : the 

 discovery of additional records would be particularly welcome. 



Fossil Plants as Tests of Climate. 



I now propose to intercalate a few words on another question of general 

 interest. Nearly forty years ago I wrote an essay on a prescribed text, 

 ' Fossil Plants as Tests of Climate,' an essay which was mainly a compila- 

 tion and not an original contribution. It is unnecessary to remind my 

 audience that fossil plants of many different ages frequently occur in 

 unexpected and, from some points of view, very inconvenient places, where 



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