CHAP. LXXIX THORNY SAVANNAH 295 



surface as to be accessible to the roots, then Caa-Tinga forest may remain 

 green throughout the dry season. 



In the neighbourhood of Lagoa Santa, on calcareous soil, Wanning l 

 found bushland composed of Cactaceae and other thorny bushes. 



On the eastern side of the Peruvian Andes, at a considerable altitude, 

 the northern slopes are, according to Ule, 2 clothed with thorn-forest 

 which is essentially composed of Cactaceae. 



In various other parts of America the presence of cactaceous bushland 

 is asserted by various writers. In America Cactaceae may replace the 

 succulent euphorbias of the Old World. 



Bamboo-bushland. 



Bamboo-bushland is a form of vegetation represented, for instance, 

 on dry uplands in the East Indies. Low thorny bamboos grow socially, 

 interlacing with one another, clothing the ground with their fallen leaves, 

 and sometimes excluding all other plants. Here and there in their 

 company are Feronia and Aegle (two of the Aurantieae), rhamnaceous and 

 mimosaceous shrubs, cactus-like species of Euphorbia, the asclepiadaceous 

 Calotropis procera, and others . Also on the Andes and other South American 

 mountains bamboo-bushland occurs, and sometimes consists ofChusquea 

 aristata, which may extend almost up to the perpetual snow-line. 



The above-mentioned Calotropis procera is a shrub possessing large, 

 stiff, roundish, glaucous leaves, and abounding in latex. In Asia and in 

 Africa, over a large extent of country surrounding Lake Chad, it produces 

 the so-called ' oc/wy-vegetation '. It has been introduced into America, 

 and is thus encountered in many spots in the West Indies and Venezuela, 

 where it thrives wonderfully in the burning sun on the driest of soils. 



CHAPTER LXXX. TRUE SAVANNAH 



SAVANNAH is associated with moderately rainy tropical places ; 

 most closely allied to grass-steppe, it owes its distinction from this 

 solely to the tropical climate. The vegetation has only one resting 

 period the dry season during which it shows itself yellowish-grey 

 and parched, though by no means devoid of flowers. The plants are 

 endowed with xerophytic epigeous organs, and withstand this dry season, 

 during which the savannah is often devastated by fires. The rainy 

 season coincides with summer ; at its commencement all the vegetation 

 becomes fresh-green, and there is a great increase in the display of flowers ; 

 especially those savannahs that have suffered from fires rapidly clothe 

 themselves with fresh-green verdure and a wealth of blossom. 



The majority of the plants are tall grasses, which have coarse and 

 stiff leaves, and usually grow in tufts to a height varying from a third of a 

 metre to a metre. When the vegetation is not too tall, between the tufts of 

 grass one can see the soil, which is usually red clay. But in addition to 

 the grasses many Cyperaceae occur in certain savannahs (some savannahs 

 are flooded during a part of the year), for instance in Guiana ; also 



1 Warming, 1892. * Ule, 1900. 



