206 ME J. BALL ON THE FLORA OF NORTH PATAGONIA 



differ much from that of Bahia Blanca, where we find the fol- 

 lowing temperatures as the result of 20 years' observations : — 



o 



Three summer months 75*6 Fahr. 



Three winter months 46 - 2 „ 



Mean of the year 594 „ 



This at once shows that the climate is eminently of a tem- 

 perate character; and this conclusion is fortified by the fact that 

 in 20 years the mean maximum temperature of the year was 

 100°'7 F. * and the mean minimum 26°-8 F. A very similar 

 climate is to be found in Europe in the corresponding latitude 

 about 100 miles east from the coast of Portugal towards the 

 Spanish frontier. If further proof were requisite, it is to be 

 found in the fact that wheat is very productive, and the vine 

 thrives in the valley of the Bio Negro. As already remarked, 

 the dryness of the climate does not account for the poverty of 

 the flora. As is well known, the opposite coasts of extratropical 

 South America present exactly opposite conditions as regards 

 the distribution of moisture. In travelling southwards on the 

 west coast you pass from the rainless zone of Peru and the 

 extreme dryness of Northern Chili to the climate of Central 

 Chili, where at Yalparaiso the annual rainfall is only 13'6 inches, 

 yet supports a varied flora, including a good many indigenous 

 trees whose structure has been adapted to the climatic conditions. 

 The rainfall increases very rapidly along the southern coast of 

 Chili till it reaches a maximum, probably about 42° S. lat., of 

 from 130 to 140 inches a year. 



On the Atlantic coast you find in South Brazil, about 26° S. 

 lat., an annual rainfall of about 90 inches, which at Monte Video 

 is already reduced to about one half, and at Buenos Ayres, less 

 exposed to the direct influence of the Atlantic, is not more than 

 35 inches. But this, it will be remarked, is nearly three times 

 the fall at Yalparaiso, in the same latitude, on the west coast. 

 At the hilly station of Tandil, not far from the sea, though 

 further south by three degrees, the rainfall is the same as at 

 Buenos Ayres ; but at Bahia Blanca we find only a fraction less 

 than 20 inches, and Dr. Hann gives a return for one year from 

 the banks of the Chubat showing a rainfall of 17 inches. There 

 * The comparatively high maximum temperature given for Bahia Blanca 

 may depend on local causes or some defect in the protection of the thermo- 

 meter from radiation. At Buenos Ayres, more than 4° nearer the equator, the 

 raean yearly maximum is 94° F. 



