- [Footnote: R. caucasicum. Decandolle found the Rhododendron ferrugineum
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 elevation. 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 flowering Compositæ 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 repetition of resembling or almost similar forms in countries separated 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 Rafflesieæ, separated from the Cytineæ, 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 phænogamous plants occur now and then sporadically on rocks which remain free from the general]*
