298 PSILOPHYTES SECT, xm 



thanks to floods caused by the Orinoco ; yet the prolonged dry season 

 gives to the vegetation a xerophytic stamp that is obvious, though its 

 details have not been investigated. 



Patanas. 



The patanas of Ceylon, according to Pearson, 1 are xerophytic grassy 

 slopes and plains of considerable extent, covered more especially with 

 various species of grasses which, to some extent, belong to the same 

 genera (Panicum, Paspalum, Sporobolus, Aristida, and others) as those 

 on savannahs and pampas. Trees are almost entirely represented by com- 

 paratively few individuals belonging to two species (one myrtaceous and 

 one euphorbiaceous). There are both dry and moist patanas. There seems 

 to be no doubt that the dry patanas, which occupy altitudes 

 less than 4,500 feet, are closely allied to American savannahs. And, 

 just as in the case of these, various theories have been promulgated 

 to account for the existence of extensive, comparatively barren, patana- 

 areas in the midst of the luxuriant subtropical growth of the montane 

 region. Grass-fires appear to play an important part in the matter ; 

 nevertheless, the peculiar climate must also be blamed for such conversion 

 of savannah-forest into savannah. Above the altitude of 4,500 feet there 

 appear moister patanas which have a sour humus soil, and may be com- 

 pared with moor-formations in temperate climes. 



Lalang-vegetation. 



In eastern Asia there are certain scrub-like associations of lalang- 

 grass, Imperata arundinacea. 2 In Java there is no weed more resistant 

 and pernicious than this grass, which is I or 2 metres in height and seizes 

 upon places where forest has been destroyed. It is doubtful whether or 

 no lalang-vegetation, which can be found interspersed with trees, is most 

 closely allied to savannah. 



African Savannah. 



African savannahs in many places appear very similar to those of 

 South America. Pechuel-Loesche 3 describes such savannahs in the 

 Congo, and terms them campine. In East Africa Engler 4 distinguishes 

 several associations (or possibly formations) belonging to savannah : 



(i) Treeless grass-savannah, which is in turn divisible into 



(a) Low grass-savannah formed by low grasses. 



(b) Tall grass-savannah formed by tall grasses. According to 

 Passarge 5 grass-savannah, without trees, occurs in the back country of 

 Kamerun only on plateaux. 



(ii) Bush-savannah occupied by grasses, shrubs, and little trees. 



(iii) Tree-savannah with tall trees, among which Adansonia digitata 

 is a veritable giant that is widespread over Africa as a whole. The trees 

 of African savannahs are deciduous. 



In regard to ' tree-steppe ' (the ' veld ') in Rhodesia, readers should 

 consult the work of L. S. Gibbs. 6 



1 Pearson, 1899; Holtermann, 1906. * Junghuhn, 1852-4. 



Pechuel-Loesche, 1882. * Engler, 1895 ; see also 1906. 



5 Passarge, 1895. L- S. Gibbs, 1906. 



