296 PSILOPHYTES SECT, xiii 



numbers of perennial herbs and undershrubs occur ; and, in contrast 

 with true steppe, shrubs and trees present themselves and are accompanied 

 by a few lianes and epiphytes. 



There is in reaUty a gradual transition from grass-steppe to savannah 

 (which is termed campo by the Brazilians). Those canipos that show 

 the greatest abundance of trees are termed by the Brazilians campos 

 serrados, which are low, open, sunny forests, composed of bent and 

 tortuous trees together with a rich vegetation of grasses, perennial he^bs 

 and small scattered shrubs that cover the ground. 



The vegetation is xerophytic,m many places because of the dry season 

 that lasts for months and (in contrast with that of steppes in the Northern 

 Hemisphere) coincides with winter, during which often no rain falls and 

 dew appears to be the sole atmospheric source of water. But the xerophily 

 is also due to the dry continental climate in general. The xerophytism 

 is expressed in the features recounted in the following paragraphs, which 

 more especially refer to the best-known South American savannahs 

 the Brazilian campos} 



A. TROPICAL SAVANNAH 



Brazilian Campo. 



With the exception of a small percentage the plants are perennial. 

 This we must attribute to the suppression of annual plants in the struggle 

 with tall, dense, perennial plants, also possibly to savannah-fires, and to 

 other causes. 



Bulbous, tuberous, and true succulent plants are much more uncom- 

 mon than in steppe, at least in American savannahs ; this is certainly 

 due to the circumstances that there is not such a short, suddenly com- 

 mencing vegetative season, nor such a prolonged and extreme dry season 

 as are met with in desert. 



The grasses forming the main mass of the vegetation are caespitose, 

 but only very rarely produce runners ; their leaves are usually narrow, 

 stiff, rough, hairy, and sometimes encrusted with wax ; and some are 

 tunic-grasses.^ 



The perennial herbs, as well as many of the undershrubs and shrubs, 

 exhibit a pecuUar type of growth, for they produce under the soil tuberous, 

 irregular, woody bodies {xylopodia),^ which apparently consist of stem 

 and root, but are mainly of a stem nature,^ and send up numerous, usually 

 unbranched or feebly branched, shoots. 



The caespitose mode of growth is also very common among woody 

 species ; individual shrubs may extend over areas several square metres 

 in surface. 



Runners and epigeous travelling shoots are wanting or, in any case, 

 very rare among the herbs. 



The trees throughout are low in stature, the tallest in the densest 

 campos being only about the height of our orchard-trees, and resembling 

 these in their tortuous trunks and branches : their cortex generally 

 includes very thick, light cork, which exhibits long cracks and is often 

 blackened by fires .^ 



^ Warming, 1892. ^ See p. 116. * Lindman, 1900. * See p. 124. 



^ Figured by Martius (1840-7) and by Warming, 1892. 



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