Chai\ V] TROPICAL DISTRICTS WITH DRY SEASONS 347 



Pechuel-Losche gives the following vivid picture of the West African 

 savannah : — 



' Many of these characteristic plants are developed only as gnarled and 

 deformed shrubs or dwarf-trees, but many also as lofty trees, some species 

 even ranking among the giants of the vegetable kingdom. They all, 

 however, have this in common, that they thrive only in the open country, 

 in the sunny, well-aired, and dry grassland ; it is true, that in places they 

 may combine to form light groves and resemble the thin oakwoods of our 

 pasture-lands, but they never appear in the form of forests. On the 

 contrary, they perish beyond recall in the cover of a well-grown forest, and 

 therefore inhabit neither fringing-forest nor rain-forest. Yet they occur, 

 not infrequently, on the borders of the savannah, where grassland begins.' 



The majority of the trees of xerophilous woodland and savannah are of 

 low stature, with a relatively thick stem, which is usually invested with an 

 extremely fissured thick bark ; the crown is frequently arranged in tiers 

 (Fig. 184), more often however it is umbrella-shaped, and may even be 

 flattened almost like a disk (Fig. 185). Umbrella-trees figure in all descrip- 

 tions of the savannah and of the open forest-formations of the tropics, 

 I have seen them determining the physiognomy of the vegetation in the 

 savannah of Venezuela, and also occurring in the alpine savannah of Java, 

 which will be subsequently described. Warming portrays them, although 

 in less regular form, in connexion with the campos of Brazil. Hans 

 Meyer says of the East African savannah : ' Whether a tree have a single 

 stem, or like a shrub ramifies from close to the ground, in either case it 

 strives first to grow as high as possible and then to expand horizontally, 

 like a mushroom or an umbrella. It is always fiat above as if it were 

 clipped. Thousands and thousands of these usually greyish-brown 

 umbrella-trees, scattered over the grass, through which the red soil gleams 

 and which is brown during the greater part of the year, impart a peculiar 

 physiognomy to the landscape 1 .' Brandis mentions as characteristic of 

 the open, dry bush-formations of Southern India, Acacia planifrons 

 (Fig. 126), called umbrella-thorn because its crown, consisting of a mass of 

 twisted knotty branches, thorns, and finely pinnate leaves, spreads out at the 

 top of the stem like an umbrella. That the umbrella-form is an adapta- 

 tion to the climate appears from the fact that it occurs under similar 

 external conditions in representatives of very different families, for instance 

 the Mimosaceae, Caesalpiniaceae (Cassia), Burseraceae, Myrtaceae. As 

 a protective device against excessive transpiration, such as might be 

 expected in an open xerophilous formation, this spreading out of the foliage 

 appears to be highly unsuitable. As a protection against the mechanical 

 and desiccating action of the wind, it is, on the contrary, proper to the end 

 in view, as it offers a narrow edge to the force of the wind. It is evident 



1 Engler, op. cit., p. 58. 



