2 PATAGONIAN EXPEDITIONS: BOTANY. 



The mighty chain of the Andes, the prevailing westerly and southwest- 

 erly winds, and the influence of the Pacific Ocean are the chief factors 

 regulating the climate of this region. In the extensive archipelago and on 

 the western slope of the Cordillera, as might have been expected before- 

 hand, the climate is decidedly maritime. The rainfall is considerable and, 

 though not definitely ascertained, it may amount to about three meters 

 per annum, and fog is the rule. In the southernmost part of the coast dis- 

 trict severe frosts and snow are not uncommon, while in the northern sec- 

 tion even a slight frost is very rare and snow does not occur in the islands 

 and coast-district proper. 



On the other hand, the eastern slope of the Cordillera naturally has a 

 much drier climate, with far greater extremes of temperature for the sum- 

 mer and winter months than in the coast district, snow not being uncom- 

 mon. Farther east the moisture of the air rapidly decreases and the 

 steppes proper have an extremely dry climate. Judging from my own 

 experience in the neighborhood of Lake Nahuel-huapi, the lowest winter 

 temperature is not below 10 C. (14 F.). 



The differences of climate on the two sides of the Cordillera produce a 

 complete difference in vegetation between the two slopes. In the damp 

 coast district very dense forests predominate, composed chiefly of ever- 

 green beeches with small coriaceous leaves, while the forests of the eastern 

 slope are thin and park-like, also composed of beeches, but these have 

 deciduous leaves. The other vegetation of these two sections shows 

 contrasts quite as striking. Farther eastward the park-like forests of 

 deciduous trees are replaced by the Patagonian steppe. From what I 

 saw in the upper Aysen valley, the boundary line between the evergreen 

 and the deciduous beech forests is very marked ; they do not interosculate 

 with each other. The case is different, however, with the deciduous forests 

 and the steppes, in so far as smaller steppes are occasionally met with in 

 the forest region long before the wide, unbroken plain is reached. But 

 the limit between forest and steppe appears in all cases to be well defined, 

 the transition from one to the other being quite sudden. West Patagonia 

 may accordingly be divided into three belts, each running parallel with 

 the Cordillera and each with a markedly different vegetation : ( i ) the 

 rainy district, comprising the archipelago and the western slope of the 

 Cordillera, the vegetation of which may be termed the community of ever- 

 green beeches; (2) the district on the eastern slope of the Cordillera, with 



