CiiAi'. n riTARACTl'RS OF THE TROPICAL CLIMATE 2.37 



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

 Ochnaccae, Dipterocarpaccae, Bixaccac, also the Tcrnstroemiaceae, which 

 includes some mesothernis, and the i\Iarcgraviaccae, consisting of tropical 

 American lianes and epiphytes. The tropical Violaceae are mainly woody 

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

 thaccae are prominent in the eastern tropics. 



Of the Coluviiiifcrac, the purely megathermic Bombacaccac arc con- 

 spicuous for their large dimensions, especially tiie 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 Gnihialcs arc of less significance. The Oxalidaceae, Tropaeolaceae, 

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

 Indies, are chiefly represented b\- herbaceous plants ; the Geraniaceae are 

 almost absent. 



The Tcrcbiiitliiuac 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 Acsadiuae 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 Frauguliiiac 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 Tricoccac are main!}- 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 

 ^enus Croton. 



The largest family of the Uinbelliflorac, 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 

 ^ornaccae also occur solely in the highlands, whilst the Araliaceae include 

 epresentatives in the lowlands as well. 



Of the Saxifraginae, the Crassulaceae, Saxifragaceae, Hamamelidaceae, 

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

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



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

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

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



The Passijloriuac are almost exclusivel}' megathermic, and are repre- 



