410 MESEOSERE AND PALEOSERE. 



and Wdkhia, and a forest climax of Noeggerathiopsis, Cardiocarpus, and Otto- 

 karia, etc. 



The life-forms of these three climaxes strongly suggest that the latter formed 

 three zones about the glacial centers, and constituted a clisere, which shifted 

 back and forth during glacial-interglacial cycles, in the manner already indi- 

 cated for the Pleistocene. Such a shifting is further indicated by the fact that 

 the Glossopteris vegetation had moved northward through Asia and Africa, and 

 into northern Europe, by the end of the Permian. The lack of detailed 

 knowledge makes it impossible to follow the movement of the Permian clisere, 

 but the cross-section of the Permian formations of Australia shown in figure 

 43 strongly suggests the occurrence of a progressive and regressive movement 

 for each of the 9 or 10 glacial-interglacial cycles. It is theoretically probable 

 that the zones of the Glossopteris flora were developed in the Paleozoic climax, 

 and that a reUct zone or mass of the latter persisted around the Glossopteris 

 climaxes during much of the Permian. This is supported by the fact that coal 

 stases representing interglacial phases occur between the boulder-beds of the 

 glacial intervals. Hence, it is not improbable that the Permian clisere con- 

 sisted of four climax zones, which behaved essentially like those of the Pleisto- 

 cene during each advance and retreat of the ice in the various centers. While 

 the floras of the two cliseres were wholly different, the life-forms were similar, 

 and the course of each clisere and its included seres must have been much 

 alike in these widely separated periods. One striking difference, however, 

 should be noted. This is that the ice centers of the Permian apparently devel- 

 oped in the midst of a luxuriant climax which covered the globe far toward the 

 poles. In the case of the Pleistocene, on the contrary, circumpolar zones 

 had long been in existence. Hence, the first advance of Pleistocene ice brought 

 about the shifting of climax zones and the burial of the successive tundra 

 zones. On the other hand, the formation of the ice-mass in the various 

 Permian centers either overwhelmed the existing vegetation and caused its 

 differentiation into climax zones, or, more probably, the accumulation of the 

 ice was preceded by a gradual refrigeration of the climate, and a concomitant 

 differentiation of climaxes, so that the ice finally buried a tundra-like nucleus, 

 and not the original Paleozoic climax. At the close of Permian glaciation, its 

 effects in tropical and subtropical regions disappeared gradually, and the zones 

 about the ice centers had probably all disappeared by the Jurassic, except as 

 they may have moved upward on high mountains. It seems highly probable, 

 however, that the restricted polar zones of the Paleophytic had received a 

 considerable emphasis, which persisted throughout the Mesophytic and Ceno- 

 phytic, though with considerable modification. In the case of the Permian 

 center on the Atlantic coast of North America, it is probable that cold or arid 

 conditions may have persisted, as they did in the Great Plains region. This is 

 suggested by the great development of cycadeans in both, and by the early 

 appearance of angiosperms on the Atlantic Coast. 



The movements of the Permian clisere must have produced a long and com- 

 plex cosere, in which the normal serai development was repeatedly truncated 

 by preclimaxes, or augmented by postclimaxes. A close scrutiny of the inter- 

 glacial coal-beds of Australia should determine whether these are mere stases, 

 corresponding to the prisere of a particular climax, or costases in which the 

 successive climaxes of the clisere are recorded. From analogy with the Pleis- 



