G. R. Wieland — Polar Climate iii Time. 409 



With regard to tlie period of an assumed polar origin or 

 implantation of life, needless to say little can be said from the 

 purely historical view in so far as now known. In general the 

 all sufficient assumption is that consolidation of the continents 

 went on apace, and that there was a continuous dispersion of 

 increasingly diverse forms from the slowly enlarging and more 

 equable polar areas towards the borders of the lessening trop- 

 ical belt over-hot for life. Even though the glohe was never in 

 the white hot conditiony this was still doubtless the case, and 

 the presumption is strong that coupled with eccentricity the 

 same progressive climatic changes already mentioned played 

 their part even in the ancient period, culminating in the uni- 

 versal tropical conditions of the Paleozoic to which the unim- 

 peachable geophysical and paleontological record carries us 

 back. But it is, of course, not possible to now trace out the 

 actual march of events in the Paleozoic, abundant though its 

 fossil forms may be. It may only be remarked that the great 

 preponderance of aquatic animals and spore-bearing plants 

 made the distribution of Paleozoic life easy, and rapid, and 

 general, facts which aside from the scanter record render it 

 very difficult to reach conclusions concerning any invasion of 

 polar forms so far as recorded in fossil florge and faunae."^ 



In general it may be said that in the Devonian and Lower 

 Carboniferous most plant forms are, so far as present, more or 

 less ubiquitous. During these periods the Equisetales, Lyco- 

 podiales, Filicales, Sphenophyllales, Cycadofilices, and Cordai- 

 tales appear to reach a high degree of specialization and for 

 the greater part a cosmopolitan distribution. These general- 

 ized floral conditions were, however, interrupted in the Permo- 

 CarboniferoLis by the appearance in the southern hemisphere, 

 mainly below the tropic of Capricorn, of a new and simpler 

 type of flora than that continuing to flourish and develop in 



snow" {Sphcerella nivalis) of the Arctic regions shows us that in the old 

 worn out and frigid stage of a planet life may still be present. 



The life of hot springs affords an example of low organization at the 

 opposite temperature extreme. 



* It is true that many large seeded plants existed, but their seeds would 

 readily be carried from island to island, when not too distant, bearing in 

 mind the much freer circulation of ocean drift among the Paleozoic islands. 

 An excellent example of the ease with which the ferns make their way is 

 afforded by the isolated occurrence of Adiantum Cajjjiillis Veneris along a 

 stream fed by thermal waters in the Southern Black Hills, far beyond its 

 utmost normal north-limit. This shows how readily spore-bearing plants 

 transplant themselves to great distances and to strange places. Nor may the 

 new station for the "Adder's Tongue," Ophioglossxim Vxdgatum,xecexxt\j 

 found in Iceland, mean that at this point a last stand is being made against 

 the cold that has driven this fern from its original boreal home, but just as 

 readily that it has long since during glacial times been pressed far to the 

 south, and that its spores have again been wafted northward from either 

 Eurasia or America. 



