244 ZONES AND REGIONS [Pt. Ill, Sect. I 



external conditions, some of them lose their foliage even before the end 

 of the rainy season, others shed their leaves at the commencement of the 

 dry season, others again do this quite gradually in the course of several 

 months, and lastly others remain in full leaf until the opening of the resting 

 buds. In some trees even, according to Warming, leaf-fall is entirely 

 suspended in many of the years. The variety in the scene is further 

 increased by the fact that isolated evergreen trees are frequently scattered 

 about the deciduous forest. 



Such distinctions, however, are only exhibited in places where the dry 

 seasons are either not very long or not quite without rain. I found the 

 dry savannah-forest bordering on the llanos of Venezuela (Province of 

 Maturin), except for a little evergreen tree, Rhopala complicata, just as 

 bare of foliage as a German broad-leaved forest in winter ; it formed the 

 most striking contrast to the narrow but dense strips of forest which had 

 retained their foliage along the water-courses. 



Grasslands within the tropics, occurring chiefly in the form of savannah 1 , 

 during the dry season, if not burned by the usual fires, appear clad with 

 dry straw-like grasses, among which only isolated plants are green and 

 flowering. A striking contrast to such a grassy covering is formed by dry 

 blocks of rock, which are burning hot in the sun, with their vegetation 

 of succulent plants, and other evergreen xerophytes, such as Cactaceae, 

 Bromeliaceae, Orchidaceae, which indeed usually blossom in the dry 

 season 2 . 



Warming describes the connexion between vegetation and the season 

 of the year in the campos of Minas Geraes in Brazil, in the following 

 manner : — 



Winter (May to July. Coldest and driest). Grass on the campos like straw. Leaf- 

 fall begins, but continues into the spring months. Some trees already lose all their 

 foliage, but some do not do this until the spring. Leaf-fall is much more complete 

 and general in the campos (savannahs) than in the forests. 



Spring (August to October). Increase of humidity and heat ; in October the rains 

 usually begin. The leaf-fall continues and becomes more general. During these 

 months most trees lose all their foliage, but display the young leaves simul- 

 taneously, or even a little earlier, so that the forest always remains green. Most 

 of the leaves remain for twelve to fourteen months on the trees, somewhat longer 

 in the forest than on the campo. Some stems retain their foliage for twenty-four 

 months, or even longer. Considered generally, the production of foliage continues 

 for half a year ; longer in some species, shorter in others. The new leaves develop 

 before the commencement of the rain. 



Swnmer (November to January). Rainy season. The leaf-fall has stopped. 

 Many species produce a second crop of leaves. Some appear to produce three 

 generations of shoots annually. 



1 See p. 162. 2 I observed this in Venezuela. 



