244 PLANT RELATIONS. 



coloration, reach their culmination in the Central West, 

 in Southern Illinois, Central and Southern Indiana, Ohio, 

 and Kentucky. 



168. Evergreen foliage forests. The word foliage is in- 

 troduced to distinguish these forests from the ordinary 

 evergreen forests which are coniferous, and which do not 

 display hroad leaves. The evergreen foliage forests are 

 chiefly characteristic of tropical regions, but occasionally 

 they are represented in temperate regions, notably of South 

 America. The conditions which especially favor them are 

 abundant precipitation and great heat. These rainy forests 

 of the tropics may be regarded, as Warming says, ' ' as the 

 climax of the world's vegetation/' for the conditions in 

 which they are developed favor constant plant activity at 

 the highest possible pressure. Such great forest growths 

 are found within the region of the trade winds, where 

 there is heavy rainfall, great heat, and rich black soil. So 

 abundant is the precipitation that the air is often saturated 

 and the plants drip with moisture. In such conditions 

 pure forests may occur, characterized by such tree forms as 

 the tree ferns, palms, or bamboos. Only the great mixed 

 tropical forest will be considered. The main characteris- 

 tics are as follows : 



(1) Absence of simultaneous periodicity. Perhaps, the 

 most striking feature, in contrast with the deciduous 

 forests, is that there is no regular period for the develop- 

 ment or fall of leaves. Leaf activity is possible through- 

 out the year, and there is no time of bare forest, or of 

 forests just putting out leaves. This does not mean that 

 the leaves persist indefinitely, but that there is no regular 

 time for their fall and formation. Leaves are continually 

 being shed and formed, but the trees alwriys appear in full 

 foliage. 



(2) Density of groivtli. Such an area is remarkably 

 filled with vegetation, stratum after stratum occurring, 

 resulting in gigantic jungles. The higher strata may be 



