It is cosmopolitan in distribution, but the majority of the species are confined to the temperate and colder parts of the northern hemisphere and many are arctic or alpine.
Most stations in the northern hemisphere have a conspicuous maximum at midsummer with little thunder in winter.
The difference between the Glossopteris flora and those which have left traces in the Upper Gondwana rocks of India, in the Wianamatta and Hawkesbury beds of Australia, and in the Stormberg series of South Africa is much less marked than that between the PermoCarboniferous flora of the northern hemisphere and the succeeding Mesozoic vegetation.
As a rule the genera of the northern hemisphere differ from those of the southern.
If mountains serve as barriers which arrest the migration of the vegetation at their base, their upper levels and summits afford lines of communication by which the floras of colder regions In the northern hemisphere can obtain a southern extension even across the tropics.
In the northern hemisphere to the south of the zone of greatest frequency, the part of the sky in which aurora most generally appears is the magnetic north.
And Figure 18 shows that GW, represented by a northern hemisphere temperature anomaly, is an important factor in the high annual CET values since 1988.
Thus we have in the northern hemisphere the Sahara desert, the deserts of Arabia, Iran, Turan, Takla Makan and Gobi, and the desert regions of the Great Basin in North America; and in the southern hemisphere the Kalahari desert in Africa, the desert of Australia, and the desert of Atacama in South America.
Further, all water particles when moving undergo a deviation from a straight path due to the forces set up by the rotation of the earth deflecting them towards the right as they move in the northern hemisphere and towards the left in the southern.
We cannot yet say, however, that the deposits are exactly contemporaneous, and the great climatic variations that have taken place in the northern hemisphere during the existence of our living flora should make us hesitate to correlate too minutely from the evidence of plants alone.