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 

 crrowth, 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 Avicntaccae 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 arc- 

 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 Urticiucac are extremely important in the tropical zones. The 

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

 dnd 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 Polygoiiiiiac, 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 Ccnirospcnnac 

 namely Caryophyllaceae and Chenopodiaceae, are almost exclusivelj 

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

 Amarantaceae are very numerous as inconspicuous herbs and men 

 rarely as woody plants. The Phytolaccaceae and Nyctaginaceae ar 

 mainly tropical American. 



The most important family of the north temperate zone among th^ 

 Polycarpicae, that of the Ranunculaceae, is mesothermic and microthermic 

 and therefore scarce!)- represented witliin the tropics except on higl 

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

 temperate zone. The most important family of the group witliin th 

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

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

 tropical families of the Anonaceae, Myristicaceae, Monimiaceae, and, i 

 contrast with the allied mesothermic Berbefidaceae, the family of th 

 Menispermaceae, include many woody plants. 



The tropical Rhocadinac are almost restricted to the Capparideae. Th 

 few Cruciferae are mostly mountain forms. 



Among the Cistiflorac are many purely megathermic families of wood 



