CiiAP. V] TROnCAL DISTRICTS WITH DRY SEASONS 347 



Pccluicl-Losclic gives the following vivid picture of the West African 

 ■savannah : — 



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

 deformed shrubs or dwarf-trccs, 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 thc)- thrive only in the open country, 

 in the sunnj-, well-aired, and dry grassland : it is true, that in places they 

 ma)- 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. 1^14), more often however it is umbrella-shaped, and may even be 

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

 tions of ilic savannah and of the open forcstforviaiions of the tropics. 

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

 savannah of \^enezuela, and also occurring in the alpine savannah of Java, 

 which will be subsequently described. Warming portraj-s 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 flat 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 landscaped' 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 



' Engler, op. cit., p. 5S. 



