14 



THE FACTORS 



[Part I 



afforded by the bark of trees in a virgin forest, the solfataras, and the alpine 

 highlands. Yet in West Java the vegetation of these habitats is, to a large 

 extent, composed of identical species of xerophytes, which are completely 

 absent from other habitats that have a greater physical resemblance to those 

 in question but are hygrophilous. Thus, for instance. Vaccinium polj'anthum 



(Agapetes rosea, Jungh.), Rho- 

 dodendron javanicum, and R. 

 retusum grow as epiphytes in 

 the virgin forest, as terrestrial 

 plants in the treeless alpine 

 region and in solfataras ; Ficus 

 diversifolia is an epiphyte in 

 the virgin forest, a terrestrial 

 shrub in solfataras ; Vacci- 

 nium varingiaefolium, Gaulthe- 

 ria leucocarpa, Myrsine avenis, 

 Tetranthera citrata inhabit the 

 treeless alpine region. All 

 these plants have conspicuous 

 xerophilous characteristics. The 

 same agreement is found in 

 Japan between the vegetation 

 of the solfataras and that of 

 the much higher alpine region. 

 The conditions of life on the 

 bark of trees, in the moderately 

 warm virgin mountain-forests, 

 and on the hot saline sea-shore 

 are still much more dissimilar 

 than in the cases cited above. 

 And yet there is at least one 

 plant that grows in both habi- 

 tats as well as in the solfataras, 

 but nowhere else — the bushy 

 Ficus diversifolia. Forming the 

 first vegetation on the dry lava- 

 fields of Gunong Guntur, which 

 are fully exposed to the sun's 

 rays, at about i,ooo meters above sea-level, I also found the Rhodo- 

 dendron javanicum mentioned above — elsewhere, an epiphyte in the 

 virgin forest, a terrestrial plant only in the solfataras and on alpine 

 highlands — side by side with orchids and ferns which are elsewhere 

 epiphytic. 



Fig. 1 6 a. Xerophilous structure. Dry sttbsiratuin 

 (epiphytes). Codonanthe sp. (Gesneraceae). Section 

 of an old leaf with voluminous aqueous tissue. Mag- 

 nified 55. Natural size shown below. From nature. The 

 lower figure is inverted. 



