:88 PLANT GEOGRAPHY 



the same time the large air-spaces will facilitate rapid 

 transpiration when the temperature rises, and the ever- 

 green condition will enable photosynthesis to occur 

 whenever light and warmth are sufficient. The shorten- 

 ing of the leaf is characteristic of Alpine grasses. Tap- 

 rooted herbaceous plants, such, for example, as the 

 Dandelion and many Thistles, frequently assume the 

 " rosette " habit, with leaves closely adpressed upon the 

 soil. 



4. Flowers are in many cases markedly larger and 

 their colours more intense. 



5. The whole surface may be shaggy with hairs, as in 

 the Edelweiss. 



With regard to temperature alone, mountains within 

 the tropics clearly exhibit four zones, which may be 

 described as Tropical; Warm Temperate, with a tempera- 

 ture averaging 60-70 F. and never falling below the 

 freezing-point; Cold Temperate, where it sometimes 

 falls below that point; and Cold, where it is usually 

 below it. 



Humboldt, basing his conclusions on the observations 

 of Broussonnet on Teneriffe and his own ascent of 

 Chimborazo, drew up the more detailed subdivision to 

 which we have previously referred (p. 71.), giving mean 

 annual temperatures for nine zones, and comparing them 

 with the latitudinal zones from the equator to the poles. 

 That such a scheme will not fit all cases, whilst some 

 zones are clearly recognisable, almost vertically super- 

 posed, is well illustrated by the following passage from 

 Sir Joseph Hooker's Himalayan Journals: 



" From the deep valleys choked with tropical luxuriance to the 

 scanty yak pasturage on the heights above, seems but a step at the 

 first coup d'retl, but resolves itself on a closer inspection into five 

 belts, i. Palm and Plantain. 2. Oak and Laurel. 3. Pine. 

 4. Rhododendron and Grass. 5. Rock and Snow. From the bed 

 of the Ratang, in which grow Palms with Screw-pine and Plantain, 

 it is only seven miles in a direct line to the perpetual ice." 



The present writer has had a precisely parallel experience 

 on the eastern slope of the Andes. 



A more generally accurate subdivision, based upon 

 moisture as well as temperature, and upon the vegetation 

 as reflecting these conditions, is the following, taken, in 

 the main, from Schimper: 



