CiiAr. IV] TROPICAL DISTRICTS CONSTANTLY MOIST 305 



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

 IS Haberlandt has already stated, on trees of tiie family of Sterculiaceae. In my 

 lotes I find Sterculia spcctabilis, Miq., Firmiana colorata, R. Br., and Pter3-gota 

 Xoxburghii, Schott and End!., as specially remarkable. I have also recorded as 

 vorthy of note, Dysoxylum niollissimum and D. Kadoya (Meliaceae) ; Urostigma 

 iltissimum and Cecropia cyrtostachj'a (Artocarpaceae) ; Spathodea campanulata 

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

 pecies of Terminalia fCombretaceae). No plank-buttresses are possessed by tall 

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

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



!G. 1 43. Sterculia sp. in the botanic garden at Buitenzorg 



After Haberlandt. 



Base ot stem with plank-buttresses. 



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

 ntiaris, Lagerstroemia, Hj'menodictyon, Nauclea, and others. 



The plank-bntiycss is a pCiuUarity of trees in a tropical climate wit/i 

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

 :curs in the deciduous monsoon-forest {Fig. 189), but is not found in less 

 iimid districts. The amount of rainfall necessar)- for its appearance is not 

 t ascertained. The physiological causes of the phenomenon and its 

 jnificance to the life of the tree are still obscure. 



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

 rk is only poorly developed on most of the tree-stems in the rain-forest, 

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



