Chap. I] CHARACTERS OF THE TROPICAL CLIMATE 237 



plants, richly represented within the tropics, such as Clusiaceae, Dilleniaceae 

 Ochnaceae, Dipterocarpaceae, Bixaceae, also the Ternstroemiaceae, which 

 includes some mesotherms, and the Marcgraviaceae, consisting of tropical 

 American lianes and epiphytes. The tropical Violaceae are mainly woody 

 plants and some are even trees. Among herbaceous families the Nepen- 

 thaceae are prominent in the eastern tropics. 



Of the Cohimuifcrac, the purely megathermic Bombacaceae are con- 

 spicuous for their large dimensions, especially the great thickness of their 

 stems and the magnificence of their flowers. The allied Malvaceae, the 

 Tiliaceae, and the purely tropical Sterculiaceae, both as woody and 

 herbaceous species, are important constituents of the tropical flora. 



The Gruinales are of less significance. The Oxalidaceae, Tropaeolaceae, 

 and the Balsaminaceae, the last of which are very common in the East 

 Indies, are chiefly represented by herbaceous plants ; the Geraniaceae are 

 almost absent. 



The Terebinthinae are, in particular, of considerable significance as con- 

 tributing to the woody plants forming the floras of the drier districts. 

 The families included here are exclusively megathermic, like Meliaceae, 

 Simarubaceae, Burseraceae, or only partially so, as Rutaceae, Anacardiaceae, 

 Zygophyllaceae. 



Among the Aesculinae the Sapindaceae are mainly megathermic, the 

 Malpighiaceae exclusively so, and frequently occur as lianes. The Ery- 

 throxylaceae and the American Vochysiaceae are also megathermic, but less 

 rich in species; the Polygalaceae are represented, but not the Aceraceae. 



The Fraiigiilinac in the families of the Celastraceae, Hippocrateaceae 

 (almost purely megathermic), Aquifoliaceae, Vitaceae (notably Cissus), and 

 Rhamnaceae supply a great number of woody plants, especially lianes. 



The Tricoccae are mainly megathermic in their most important family the 

 Euphorbiaceae, and afford the tropical flora a great number of arborescent, 

 shrubby, and herbaceous species, in particular belonging to the large 

 genus Croton. 



The largest family of the Umbelliflorae, namely the Umbelliferae, is 

 almost exclusively mesothermic, so that within the tropics it is represented 

 in the mountains, but only by a very few species in the lowlands. The 

 Cornaccae also occur solely in the highlands, whilst the Araliaceae include 

 representatives in the lowlands as well. 



Of the Saxifraginae, the Crassulaceae, Saxifragaceae, Hamamelidaceae, 

 and Platanaceae are pre-eminently mesothermic and of only slight impor- 

 tance within the tropics. The Podostemaceae are tropical aquatic plants. 



The American family Cactaceae, the sole constituent of the Opuutinae, 

 has numerous representatives in the dry districts of tropical America, and 

 some common epiphytes and lianes in the rain-forests also belong to it. 



The Passiflorinac are almost exclusively megathermic, and are repre- 



