FOREST SOCIETIES. 543 



the year, so that soil moisture and atmospheric humidity, while 

 showing some variations, are relatively high throughout all seasons. 

 This with the high degree of heat maintained throughout the 

 year provides most favorable conditions for rapid and continued 

 growth. 



1026. Absence of climatic periodicity in evergreen tropical 

 forests. The absence of climatic periodicity in these ever-damp 

 tropical areas is most striking in its effect on the general charac- 

 ter of the vegetation as compared with those tropical areas where 

 climatic periodicity is present, i.e., a dry season extending over 

 a considerable period and alternating with a rainy season, as 

 well as the climatic periodicity in the temperate regions, where a 

 cold season alternates with the warm growing season. The 

 more striking effects are, ist, almost continual growth; 2d, the 

 absence of bud-scales on the buds, since there is no austere season 

 when these are needed to protect the young growing part, as is 

 the case in the dry tropical or subtropical areas, or during the 

 cold season in temperate and arctic regions; 3d, absence of uni- 

 formity in the time of defoliation : since there are no climatic changes 

 which necessitate uniformity, a tree sheds its leaves and in a few 

 days puts out a new crop; 4th, an extended flowering and fruiting 

 period for many species, so that flowering and fruit-bearing often 

 overlap in the same tree, though this does not continue through- 

 out the year; 5th, a very dense forest canopy because of the 

 favorable conditions of growth and the large size and number of the 

 leaves making the interior of the forest darker than in any other 

 forest areas, thus lessening the proportion of herbage on the forest 

 floor-, 6th, there is a relatively small amount of humus, the high 

 degree of heat and moisture favoring rapid decay of fallen leaves 

 and wood; yth, in the many structures for protection of leaves 

 against excessive wetting and the beating of heavy rains; a 

 thick cuticle and often hairy leaves are examples of adaptations, 

 while some interesting cases are known where the upper side of the 

 leaves is furrowed along the line of the veins, these uniting and 

 converging on the margin into a " gutter" which terminates on 

 the external midrib at the leaf tip, forming a drainage system for 



