tains through which no rivers opened a way to the south.The want of relationship between 

 the Reuverian and the living flora of Europe would seem to imply that, as wave after 

 wave of migration broke against this barrier, the species it brought must have perished, 

 cut off by the cold of the north behind and of the mountains in front. It was at this barrier 

 that the connexion between the present European and the Chinese floras was destroyed; 

 so that now, except in deposits such as the Reuverian, and in a lesser degree the Teglian, 

 very little trace of it is to be found. From time to time seeds were undoubtedly carried 

 across the mountains ; but it is interesting to note that the plants thus transported were 

 nearly always smalbseeded species, such as could be dispersed by birds. A few of the 

 hardiest plants, as we have already shown, managed to survive north of the mountains — 

 such forms as Quercus Robur, Corylus Avellana, and Picea excelsa — and here it is interesting 

 to note that many of these cooktemperate survivors are large*seeded forms. 



Even those plants that crossed the Alps were not however secure. They had 

 migrated into a region warm enough, but too dty for them, as are the lowlands of 

 China; where, as Wilson shows, the mountain flora is quite unable to live. Present day 

 conditions in the Mediterranean Region are unsuited to the Reuverian flora, though 

 the mean temperature probably does not differ greatly from that of Limburg in Middle 

 Pliocene times. This unsuitability of South Europe to act as a refuge for the Reuverian 

 plants was brought home to us in a curious way. The botanic gardens of La Mortola, 

 in the Italian Riviera, have an enormous collection of Warm Temperate plants, and the 

 authorities are very liberal in helping botanists. We therefore wrote to ask whether 

 they could let us have fruits of any of the peculiar mountain plants of West China. 

 Dr. Alwin Berger, though he was able to send us many Mediterranean species, only 

 one of which occurred also in the Reuverian flora, was obliged to answer our special 

 request thus: "Unfortunately I have never cared much for the Chinese and Japanese 

 Flora for our garden, as most of those plants do not like our dry and hot climate, as do 

 the plants from Australia, the Cape, Mexico, etc." In a later letter he endorsed our 

 suggestion that this unsuitability of the climate was probably one cause of the absence 

 of many of our fossil species in the Mediterranean Region. 



By the advent of the first Glacial Period almost all the warmer elements of the 

 temperate flora of Northern and Central Europe and Asia must have been swept away; 

 so that when milder conditions prevailed, these regions had to be re*colonized. But 

 colonization into a region of rising temperature could only take place from the south, 

 probably by slow migration of the smallsseeded plants northward across the mountains, 

 and from the Iberian Peninsula northward along the coast, in the direction of the preva* 

 lent wind. We have an interesting example of such colonization going on in the south* 

 west of England and Ireland at the present day. Here many Lusitanian plants, all of 

 them small*seeded, are slowly establishing themselves near the sea, and in some instan* 

 ces (Erica vagans, etc.) gradually pushing their way inland and northward. But such a 

 process is very slow, and it is not surprising that, both in Interglacial times and the 

 present, the flora of cooktemperate latitudes in Europe should be a poor one. 



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