236 ZONES AND REGIONS [Pt. Ill, Sect. I 



greater. Their characteristics are however much less striking, so that 

 a picture of vegetation essentially composed of Dicotyledones alone, 

 frequently has a great resemblance to one in the temperate zones. When 

 marked peculiarities such as those of branching, abnormal disposition of 

 the leaves towards the horizon, plank-buttresses, subaerial roots, epiphytic 

 growth, and so forth, do present themselves, they are not as a rule the 

 characters of families, but oecological adaptive features recurring in the 

 most different cycles of affinity. 



The distribution of Amentacetxe within the tropics is comparable with 

 that of Coniferae, as they form a considerable contingent of the flora in the 

 higher mountain regions outside the megathermic climate, whilst they are 

 unimportant in the lowlands. They are not completely absent ; there 

 are, for instance, some megathermic oaks in Mexico, and, according to 

 my own observations, in the forests near Singapore. 



The Urticincac are extremely important in the tropical zones. The 

 Moraceae in the first place, with the genus Ficus with its numerous arboreous 

 and shrubby species, also with the genus Artocarpus, to which belong 

 some of the commonest cultivated tropical trees, Artocarpus incisa, the 

 bread-fruit tree, A. integrifolia, the jack-fruit tree ; the Urticaceae with 

 numerous genera of usually shrubby or herbaceous species. 



Among the Polygoninae, the Piperaceae are exclusively megathermic. 

 They are represented in the rain-forests chiefly by many shrubby and 

 herbaceous terrestrial plants, as well as by root-climbing lianes and epi- 

 phytes. The Polygonaceae are limited to a few species, chiefly arboreous. 



The families that in Central Europe chiefly represent the Ccntrospcrmac, 

 namely Caryophyllaceae and Chenopodiaceae, are almost exclusively 

 mesothermic and of no importance within the tropics. On the other hand, 

 Amarantaceae are very numerous as inconspicuous herbs and more 

 rarely as woody plants. The Phytolaccaceae and Nyctaginaceae are 

 mainly tropical American. 



The most important family of the north temperate zone among the 

 Polycarpicae, that of the Ranuncuiaceae, is mesothermic and microthermic, 

 and therefore scarcely represented within the tropics except on high 

 mountains. The Magnoliaceae also are less frequent than in the north 

 temperate zone. The most important family of the group within the 

 tropics is that of Lauraceae, to which numerous forest trees, also shrubs, 

 and the common herbaceous liane-parasite Cassytha, belong. The purely 

 tropical families of the Anonaceae. Myristicaceae, Monimiaceae, and. in 

 contrast with the allied mesothermic Berberidaceae, the family of the 

 Menispermaceae, include many woody plants. 



The tropical Rhoeadinae are almost restricted to the Capparideae. The 

 few Cruciferae are mostly mountain forms. 



Among the Cistiflorac are many purely megathermic families of woody 



