158 PHYSIOGNOMY OF PLANTS. 



E. caucasicum. Decandolle found the Rhododendron ferru- 

 gineum growing singly in the Jura (in the Creux de Vent) 

 at the moderate altitude of 3100 to 3500 (3304 to 3730 E.) 

 feet, 5600 (5968 E.) feet lower down than its proper ele- 

 vation. If we desire to trace the last zone of vegetation 

 nearest to the snow line in the tropics, we must name, from 

 our own observations, in the Mexican part of the tropical 

 zone, Cnicus nivalis and Chelone gentianoides ; in the cold 

 mountain regions of New Granada, the woolly Espeletia 

 grandiflora, E. corymbosa and E. argentea; and in the 

 Andes of Quito, Culcitium rufescens, C. ledifolium, and 

 C. nivale, yellow 7 flowering Compositse which replace in 

 the last-named mountains the somewhat more northerly 

 Espeletias of New Granada, to which they bear a strong 

 physiognomic resemblance. This replacement, the repeti- 

 tion of resembling or almost similar forms in countries sepa- 

 rated either by seas or by extensive tracts of land, is a 

 wonderful law of nature which appears to prevail even in 

 regard to some of the rarest forms of vegetation. In Robert 

 Brown's family of the Rafflesiese, separated from the Cyti- 

 nese, the two Hydnoras -described by Thunberg and Drege 

 in South Africa (H. africana and H. triceps) have their 

 counterpart in South America in Hydnora americana 

 (Hooker). 



Far above the region of alpine plants, grasses, and lichens, 

 and even above the limit of perpetual snow, the botanist 

 sees with astonishment, both in the temperate and tropical 

 zones, isolated phsenogamous plants occur now and then 

 sporadically on rocks which remain free from the general 



