AN ICE AGE IN THE SOUTH

IN the southern hemisphere the vegetation was not nearly as varied, largely because the climatic conditions were less favourable. Vast areas in the south were in the grip of an Ice Age while luxuriant vegetation flourished in the north. The southern flora had no true Calamites or tree horse-tails, few giant club-mosses and few of the common seed-ferns so familiar in our coal-beds. The most abundant plant fossils are certain tongue-shaped leaves with netted veins, called Glossopteris (‘tongue fern ‘), of which there are numerous varieties. Hence the name Glossopteris flora, which has been applied to the whole assemblage of Upper Carboniferous and Permian plants of South America, South Africa, India and Australia. It has been surmised that these areas, with their very uniform flora, were formerly more or less united into one great continent, to which the name Gondwanaland has been given.

In spite of its name, it is now regarded as certain that Glossopteris was not a fern at all. It may have been a seed-fern, or it may have belonged to some gymnospermous group, but the conditions of preservation have not left us anything comparable with the coal-balls of Europe and America, and we really know little of the internal structure or of the reproductive organs of Glossopteris and its allies. Gymno-sperms were certainly well represented in the flora, and some

of them seem to have belonged to the same group as Cor-daites. The Sphenophylls were represented, and the horsetails were of more herbaceous types than the Calamites, though still unlike those of to-day.

THE SOUTH POLE PLANTS THAT SCOTT DISCOVERED THE northern and southern floras did not occupy entirely distinct territories. There was an admixture of the two in Central Africa down to Southern Rhodesia, while in Sumatra and Malay a northern flora has been found unaccompanied by Glossopteris. In south-eastern Asia Glossop-leris itself lasted on into the next era, and thence perhaps spread northwards and westwards in the early Mesozoic. But in general, the very distinctive Glossopteris flora belongs to the southern region known as Gondwanaland, which, in this era, included Antarctica. One of the most important discoveries of Scott’s last expedition to the south polar regions was of strata containing Glossopteris and other fossil plants at Buckley Island on the Beardmore Glacier, within three hundred miles of the South Pole. Evidently the climate of the Antarctic must then have been considerably warmer than at present.

We have already mentioned that the earlier Archceopieris flora flourished in Arctic regions, and many later plant-bearing deposits are known within the Arctic and Antarctic circles, so that we may be justified in regarding the present extreme frigidity of these regions as being, geologically speaking, abnormal. It would be out of place, however, to enter into a full discussion here of the questions connected with changes of climate and of the distribution of land and sea in past ages. It is necessary to mention these changes because of their influence on the distribution and evolution of plants.

The coming of an ice age in the southern hemisphere was evidently connected with the extinction of the Archccopteris flora and the rise of Glossopteris; in the northern hemisphere, the gradual disappearance of the seed-fern flora of the coal swamps was largely due to increasing desiccation. At the close of the Permian period and in part of the succeeding Triassic period desert conditions prevailed over large tracts. The break in the succession of floras seems, of course, more complete when we study only a limited area; or when conditions happen to be unfavourable for the preservation of

fossils, but the change in the vegetation was undoubtedly very great in the northern hemisphere.

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