GENERAL CONCLUSIONS. 107 



The topography is of prime importance for the distribution of the 

 vegetation, for it is the agency by which the physical conditions are 

 given their local modifications, and these modifications are in turn 

 responsible for the distribution of the forest types. Changes in the 

 topography are active, through erosion, but their operation leaves the 

 relief of the mountains essentially unaltered as they are gradually worn 

 down. There is no respect in which the progress of physiographic 

 change alters the adjustment of physical conditions or the distribution 

 of the habitats, excepting perhaps the case in which a ravine may 

 broaden and eventually become a part of the larger slope down which 

 the ravine formerly drained. Although the eroding power of a heavy 

 tropical rainfall is rapidly carrying the montane region toward base- 

 level, the only discoverable outcome of the process is that the present 

 vegetation, with all of its present habitat distinctions, will gradually 

 be carried down to a level at which climatic changes will dominate the 

 history of the vegetation. The existence of two small areas of alpine 

 meadow on high peaks at the present time would indicate that such 

 has been the fate of types of vegetation that formerly occupied the 

 higher elevations. 



Any successional phenomena which might be discoverable in the 

 montane rain-forests, whether due to such physiographic change as 

 the merging of a maturing ravine into its mother slope or to such 

 climatic change as would cause a relict alpine meadow to be invaded 

 by forest, would in any case resolve themselves into a matter of the 

 gradual change of vegetation in dependence upon a gradual change of 

 physical environment. The relation of the old vegetation to its envi- 

 ronmental conditions, and the relation of the succeeding vegetation 

 to its environmental complex are both matters that would far outweigh 

 in importance the floristic and ecological features of the succession itself. 



Under the conditions of equable temperature and abundant water 

 supply which obtain in the rain-forest, there are no climatic checks 

 to the continual activity of the plants. The annual periodicities of 

 growth and flowering are, however, greatly diversified, there being 

 unbroken activity in some species and a well-marked winter season 

 of rest in others. It may be said, in general, that the former species 

 are those of tropical lowland relationship and the latter are those 

 belonging to north temperate genera. It is to the inherited differ- 

 ences of physiological constitution between these groups of plants that 

 we must look, by experimental means, to an understanding of their 

 divergence of behavior under identical physical conditions. 



The rate of growth in the montane rain-forest region is much slower 

 than it is in the vegetation of the lowlands. The uncoiling leaves of 

 tree-ferns and the leaves of some of the large herbaceous ferns exhibit 

 a rapid rate of elongation. The growth of leaves is moderately rapid 

 in the shrubs and trees which are in continuous or nearly continuous 



