CLIMATE OF MADEIRA. 135 



Those Miocene plants which represent such as are now met 

 with in the temperate zone, and do not extend into the tropics, 

 demonstrate that Switzerland had not at that time a tropical 

 climate. We find a considerable number of species in the Mio- 

 cene district the nearest allies of which now live in the plains of 

 Central Europe or in North America. Most of these, however, 

 extend their range into the warm zone : thus the common 

 bracken (Pteris aquilina) is as abundant in Madeira as in Swit- 

 zerland, and it is also found in California and Japan ; the relatives 

 of the Swiss Miocene species of Equisetum extend to the south 

 of the United States ; the Isoetes and the little pondweed occur 

 even in Brazil ; the common reed (Phragmitis) lives in Italy, on 

 the Caucasus, in Japan, and in America ; the reed-mace (Typha 

 latifolid) grows in the Crimea and in South Carolina, the 

 branched burr-reed (Sparganium ramosum) in Persia and Caro- 

 lina, and rushes in Madeira and the Canary Islands ; while the 

 red maple extends down to the south of the United States : 

 and these are all species representing Miocene forms which we 

 have classed as belonging to the temperate zone. 



With regard to other species, to which cultivation has given 

 an artificial area of distribution, it is manifest that they can 

 support higher temperatures : thus the planes and poplars and 

 walnut-trees thrive well in Madeira; and in the south of Spain 

 splendid elms and white poplars are seen side by side with 

 southern Melice and Phytolacca in the public gardens of the 

 towns. Hence the occurrence of the types of plants of the 

 temperate zone in the Miocene flora may be easily explained, if 

 we assume that at that period Switzerland had a climate similar 

 to that of Madeira. It must be remembered that the plants of 

 the temperate zone suffer much less from higher temperatures 

 than those of warm countries do from cold. Too great heat 

 does not so much limit the extension southwards of plants as 

 the great dryness of the hot season. 



The combination of types of plants of the tropical and tempe- 

 rate zones in the Swiss Miocene flora is by no means surprising, 

 as we meet with the same conditions at the present day in 

 Madeira and the Canary Islands, where the zones of distribution 

 of many southern and European forms meet ; they indicate a 



