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Ch. XLL] 



KEFEEENCE TO THE OEIGIN OF SPECIES. 



4ii* 



enjoyed cut off from all communication witli other islands, into 

 wliicli new colonists, both of the animal and vegetable worlds, 

 have been able more freely to penetrate. 



Dr. Hooker reminds us that the extinction of so many 

 species and of some genera which flourished in the Miocene 

 period in Europe, is fully accounted for by the great change 

 of climate which the temperate latitudes of the northern 

 hemisphere experienced in Pliocene and Glacial times. The 

 old subtropical species^ wliicli had long flourished in Central 

 Europe and in the regions bordering the Mediterranean, 

 gave way before a more southern flora^ but many plants and 

 not a few of the insects, w^hich were extirpated on the con- 

 tinent, may well have survived in oceanic islands which 

 enjoyed a milder and more equable temperature. To this 

 source we may probably refer those peculiar ^Atlantic types ' 

 above alluded to, which pervade all the archipelagos. We 

 are informed by Dr. Hooker that the seeds of the West 

 Indian bean-like climber Entada were floated to the Azores 

 3,000 miles by the Gulf-stream. These seeds, after such 

 long immersion in salt water, although they could not stand 

 the climate of the Azores, germinated in the Garden at Kew ; 

 from which fact we learn how easily seeds of the Miocene 

 period may have been carried uninjured by currents from the 

 Mediterranean region to any one of the Atlantic islands, 

 as none of them are so far from Europe as are the Azores 

 from the West Indies. But it is probably to birds more 

 than to marine currents that new islands owe the plants 

 which clothe them. We have already seen (p. 394) how 

 many seeds Avhicli have been swallowed by birds and ejected 

 in their dung, germinate freely, and these, if carried by a 

 land-bird driven to a new volcanic island, would soon cover 

 the unoccupied ground, until other species brought by a 

 similar mode of transport came to dispute their monopoly. 



It is not easy to conjecture how many different modes of 

 transport nature may have employed in peopling some At- 

 lantic islands. Even icebergs may have played their part in 



carrymg plants to the Azores in the Glacial period, for they 

 are now sometimes floated to latitudes farther south than 

 that archipelago, as we have already stated (Yol. I. p. 246). 



E E 2 



