GEOGRAPHICAL BOTANY. 403 



hot and dry season lasts from November until the end of 

 April. The garua, a thin mist, which is thickest in 

 August and September, reanimates the steppes from May 

 to October. It only extends 1400' high vertically in the 

 atmosphere. As long as this prevails the steppe is verdant, 

 and sends forth numerous Liliaceous forms into flower. 

 The south winds generally last throughout the entire year ; 

 and V. Tschudi considers the formation of the garua as still 

 unexplained. May they not arise, as winterly precipita- 

 tions, from an admixture of the lower trade-wind with 

 the east winds descending from the Andes, and which, 

 during the summer, are not in a condition to separate 

 the moisture from the coast trade-wind ? 



b. Internal coast-region (1500' 4000'). This com- 

 prises the fan-shaped expansion of the west valleys of the 

 Cordilleras, which, at the time of the garua, is affected 

 with a true rainy season. Mean temp, in the dry season, 

 = 29 0> 25 ; in the rainy season = 22'75. The vegetation 

 is not very luxuriant, but the cultivated tracts are extra- 

 ordinarily productive. The sugar-cane thrives well even 

 at 3600'. Of fruits, Anona tripetala (Chirimoya) and 

 Passiflora quadrangular is (Granadilla) are peculiar to this 

 region. 



c. Western Sierra (4000 11,500'), or that slope of 

 the Cordilleras which is gently inclined below, and steep 

 above, with its narrow transverse valleys. The air is dry ; 

 the nights are very cold in summer \ the prevailing wind 

 is the east. In summer the mean temperature at noon 

 is = 22'4, at night = 10 ; in winter, the mean diurnal 

 temperature is = 19. This is the region of the tropical 

 Cerealia, and that in which the potato thrives readily and 

 in profusion. Oxalis tuber osa (Oca) commences in it. 

 The Cacti are among the characteristic plants of this slope, 

 which contains but little wood. 



d. Western Cordillera, comprises the west slope of the 

 Andes above 11,000', and the east declivity of this 

 western crest as far downwards as 14,000'. It forms a 

 wild mountainous tract, containing steep rocky declivities. 



