BOTANICAL GEOGRAPHY. 445 



peculiar condition. In Italy, Dalmatia, and in Turkey, we find immediately 

 above the evergreen region, slopes abounding in forests of Central European 

 forms of trees, and other plants indigenous to this side of the Alps : angiosper- 

 mous trees, which lose their leaves in winter, even at an altitude of 1200' to 

 1500', frequently begin to denote this second Central European region. In 

 Spain, Boissier, with other authors, distinguishes two evergreen regions : a lower 

 one, which in the character of its vegetation appears to agree with the Italian 

 or Dalmatian, and reaches to 1500' in Catalonia, and to 2000' in Granada ; and 

 an upper one, which, extending from 2000' to above 5000', includes the greater 

 part of Spain, and has no analogy with any other throughout the entire south 

 of Europe. It has been shown by Schouw's investigations, that the climatai 

 cause of the evergreen vegetation of the Mediterranean lies in the aridity of 

 the summer, to which the plants of the north of Europe are not subjected. 

 Out of Spain, the latter again meet with conditions necessary for their 

 existence on the mountain-chains of the south of Europe, in the vicinity of 

 the region of clouds, where, even in the summer, the air contains mists formed 

 from its watery vapour, and where the low scale of temperature is the same 

 as in the climate of the north. The elevated plains of Spain are, however, 

 in summer even more arid than the coast-regions ; the humid and mild spring, 

 which stimulates all the plants to flower, is there succeeded by a hot and dry 

 summer and a cold winter ; the three seasons of the steppes of Russia are dis- 

 tinguished. Although this explains the fact that some plants of the plateau 

 of Spain recur in the Crimea, or on the elevated surfaces of Asia Minor, yet 

 their number is small ; for the contrast of the insular and the extreme climate 

 of the interior of the continent exerts such influence here, that the greater 

 part of the plants of Spain are not exposed to the great winter-cold of the 

 eastern elevated surfaces and steppes. Hence the greater part of the flora 

 of the plateau of Spain must consist of endemic plants, because these climatai 

 conditions do not exist elsewhere in Europe. This is still more strikingly 

 perceptible in central Spain (see the Ann. Rep. for 1843) than in Granada, 

 where the plateau-character is less developed on the mountain-slopes, and 

 the vegetation contains fewer forms. But it is clear that more plants of the 

 evergreen coast-region may occur in a climate of this kind than in that of 

 Northern and Central Europe. Returning to the observations of Boissier, he 

 estimates the region which corresponds in Granada to the plateau of Spain as 

 extending from 2000' to 4500' on the northern, and to 5000' on the southern 

 slopes. Within this region, but not far from its lower boundary, the cities 

 of Granada and Ronda are situated, where, in the winter, the thermometer 

 regularly falls 6 8 below 32 F. for a few days. At its upper limit, e. g. in 

 the village of Trevelez, in the Alpuj arras, the snow lies on the ground for four 

 months, from December to April. The summer-heat is frequently greater at 

 Granada than on the coast, but the nocturnal cooling is very considerable. 

 The distribution of the atmospheric precipitations is the same as in the lower 



