24 A MONTANE RAIN-FOREST. 



l>ut is simulated in several species in which the flown- are produced 



from the axils of the fallen leaves of the preceding year, as in EuQi nm 



marchiana, Acnistus arborescent, Mecranium purpuraecens, and Alchor- 



iK a ladfolia. Such purely tropical characteristic- as plank butt re 



and the hunching of leaves at the ends of the branches are entirely absent. 



The attenuated leaf ends or "dripping points" which have been 

 found to characterize the rain-forests of the eastern hemisphere, are 

 very uncommon in the Jamaican rain-forest, and the functional value 

 of such structures appears to have been overestimated. 1 



Only in the narrowest ravines is there a lofty and closed canopy, and 

 as one proceeds into wider ravines and from them onto slopes and 

 finally onto the ridges the canopy becomes more and more open, 

 although its general level is more uniform on the ridges than in the 

 ravines. The canopy itself has no line of demarcation from the foliage 

 of the under-trees and shrubs, resulting in an irregular and more or 

 less solid mass of foliage from the tree tops down nearly to the level 

 of the terrestrial herbaceous plants. There is, however, just above the 

 herbaceous vegetation a layer free of foliage, which in wide ravines 

 sometimes reaches as high as 10 or 20 feet (3 to 6 meters), but on the 

 slopes and ridges disappears altogether. 



The leaves of the generality of trees and shrubs are of medium or 

 small size, from about 75 sq. cm. in area in Clethra alexandri to less than 

 1 sq. cm. in Eugenia alpina (see plate 21 A). In all but three of the 

 commonest trees (Brunellia, Weinmannia, and Guarea) the leaves are 

 simple, and without exception they are firm or even coriaceous, with 

 from one to four layers of greatly elongated palisade cells and with 

 compact mesenchyma, in high contrast to the extremeh' hygrophilous 

 character of the leaves of the ferns and other herbaceous plants of the 

 forest floor. 



The floor of the rain-forest is covered with a litter of leaves, twigs, 

 and limbs, the decay of which seems to be retarded rather than accel- 

 erated by the extreme wetness maintained at relatively low tempera- 

 tures. Ants do a small amount of work in destroying dead trees 

 before they fall, and an abundance of small discomycetous fungi 

 (almost the only representatives of their group) hastens the disinte- 

 gration of the leaves and small twigs. The soil is extremely rich in 

 organic matter, but is shallow and full of angular rock fragments. 



The terrestrial herbaceous vegetation varies from extreme wealth 

 in the ravines to almost complete absence in many places on the ridges 

 where the climbing bamboo, Chusquea abietifolia, is abundant, and 

 where the amount of light reaching the forest floor is so great as to 

 permit the development of extended thickets of the scrambling ferns 

 Gleichenia and Odontosorea. In the ravines ferns form by far the most 



^hreve, Forrest, The Direct Effects of Rainfall on Hygrophilous Vegetation. Jour, of 

 Ecology, 2, 1914. 



