60 GEOGRAPHICAL DISTRIBUTION 
moister soil, produce a rich grass vegetation like that of Middle 
Europe, particularly on the benches or terraces which rise from the 
banks of the rivers. 
The frozen tundra of.the arctic region, when thawed during the 
brief spell of summer, exposes a growth of stunted grass mixed with 
mosses and lichens. Alpine summits of lower latitudes have a 
similar vegetation ; the higher we climb, the more dwarfed and 
sparse do the grasses become, until their ascent to the snow-line 
is arrested by the denudation of the rocky surface. 
In the warmer parts of both temperate zones, particularly on the 
borders of the tropics, there is much diversity in the aspect of 
gramineous vegetation. Regions of great heat, scanty rainfall, 
and dry sandy soil—the immense deserts of S.W. and Central 
Asia, the Sahara, the Great Basin of North America ; and in the 
southern hemisphere the Kalahari and Great Victoria deserts—are, 
in general, characterized by thorny shrubs and a sparse growth 
of harsh grasses, 2-3 inches to 1-2 feet high, the leaves short, rigid, 
sapless and involute. Transpiration in these desert-grasses is 
thus diminished to the lowest degree, to enable them to conserve 
their vitality during the prevalence of hot winds and prolonged 
drought. In moist localities, by springs, wadies, and in saline 
marshes, the grasses rise to several feet ; rarely, however, is there 
such a tall dense growth as the belts of Phragmites communis 
around the lakes of the Aralo-Caspian basin. Wide stretches of 
burning sand, impregnated with salt and utterly desiccated through- 
out the year, are destitute of vegetation ; but wherever there is 
ground-moisture or a little precipitation at any season, this ensures 
a growth of grasses, although perhaps of brief duration, dotted over 
the plains in tufts or patches, or forming extensive oases. 
In sub-tropical regions of moderate rainfall, followed by a season 
of drought, the grasses of dry plains, like those of the southern 
portion of the prairie region and of the western plateau of North 
America, and the pampa of Argentina, west of long. 63°, grow 
mostly in isolated clumps, 4-5 feet high, the foliage rigid and 
very scabrid. But elevated plateaux and mountainous districts, 
as in South Africa, Mexico, and S.E. Australia, produce a 
short, close and soft turf, which during the rainy months re- 
sembles the sward of a more equable climate. The grasses of 
moist rich plains attain a stature of 6-9 feet, and grow in close 
contiguity, forming thickets. A typical example of luxuriant sub- 
tropical grasses is Gynerium argenteum, the Silvery Pampas-grass, 
which grows in the rich humid soil of the eastern part of the 
Parana and La Plata plain. It would be impossible, says the 
Naturalist in La Plata, to give anything like an adequate idea of 
the exquisite loveliness, at certain times and seasons, of this queen 
of grasses, the chief glory of the solitary pampa. One may ride 
through many leagues of this grass, which spreads away for miles 
on every side, the myriads of white plumes (as high as one’s head), 
touched with varied colour, blending in the distance, and appearing 
almost like the surface of a cloud. 
