Chap. IV] TROPICAL DISTRICTS CONSTANTLY MOIST 305 



of known systematic position. The most remarkable of these structures appear, 

 as Ilaberlandt has already stated, on trees of the family of Sterculiaceae. In my 

 notes I find Sterculia spectabilis, Miq., Firmiana colorata, R. Br., and Pterygota 

 Roxburghii, Schott and Endl., as specially remarkable. I have also recorded as 

 worthy of note, Dysoxylum mollissimum and D. Kadoya (Meliaceae) ; Urostigma 

 altissimum and Cecropia cyrtostachya (Artocarpaceae) ; Spathodea campanulata 

 (Bignoniaceae) ; Vitex timorensis, V. Cofassus, V. leucoxylon (Verbenaceae) ; most 

 species of Terminalia (Combretaceae). No plank-buttresses are possessed by tall 

 trees belonging to the families Sapindaceae, Apocynaceae, Sapotaceae, or to species 

 of Myristica. Many species of the latter genus have prop-roots. Brandis mentions 



Fig. 143. Sterculia sp. in the botanic garden at Buitenzorg. Base ot stem with plank-buttresses. 



After Haberlandt. 



plank-buttresses in connexion with Bombax malabaricum and species of Vitex, 

 Antiaris, Lagerstroemia, Hymenodictyon, Nauclea, and others. 



The plank- buttress is a peculiarity of trees in a tropical climate with 

 abundant rainfall. It is not limited to the evergreen rain- forest, for it also 

 occurs in the deciduous monsoon-forest (Fig. 189), but is not found in less 

 humid districts. The amount of rainfall necessary for its appearance is not 

 yet ascertained. The physiological causes of the phenomenon and its 

 significance to the life of the tree are still obscure. 



Owing to the prejudicial effect of humidity on the formation of cork, the 

 bark is only poorly developed on most of the tree-stems in the rain-forest. 

 Stems in the rain-forest never exhibit scales of bark of such surprising 



9 HIMPER ^ 



