CHARACTERISTICS OF THE ZONES OF MOISTURE. 187 



toiy, and reaching on the north to the tropic, and the south to the 

 Victorian Alps. Here there are no Cactuses, Stapelias, Agaves, or 

 Aloes, and Crassulacese is only represented by Bryophylliim. The 

 fleshy-leaved Dicotyledons are represented by Zygophyllum, Calan- 

 drinia, two or three species of Mesembryanthemum, and several 

 Chenopodiaceae, and the fleshy Endogens by Bulbine, Of the Phyllo- 

 dineous Leguminosae there are Brachysema, Jacksonia, and not less 

 than 270 kinds of Acacia. In petaloid Monocotyledons there are Sty- 

 phandra, Patersonia, Caesia, Thysanotus, Tricoryne, and other Anthe- 

 riceae. In Cycads there are Cycas and Macrozamia, and a very peculiar 

 endemic Monocotyledonous type of similar habit in Xanthorrhoea 

 and Kingia. The Dicotyledons with large scariose bracts are repre- 

 sented copiously by Helichrysum and Gomphrena, and there is a 

 similar endemic Monocotyledonous type in Borya and Laxmannia. 

 The most abundant type of all is that of the bushes with rigid and 

 gland-dotted leaves, very abundantly represented here in Boronieae, 

 Myrtaceae, Leguminosae, Proteaceae, and Epacridaceae. 



5. The flora of the province of Atacama, which extends on the 

 west side of the Andes from the borders of Bolivia to 28 or 30 south 

 latitude, and in the heart of the Continent, Catamarca, Tucuman, 

 Cordova, Mendoza, and other provinces of the Argentine Confedera- 

 tion. Here there are no Agaves, Aloes nor Stapelias, and scarcely 

 any Crassulaceae, but a good many Cactuses, whilst the cactus- 

 like Euphorbias are represented by one, and the Mesembryan- 

 thema by two or three species. Amongst characteristic Xerophilous 

 types are Calycereae, an order confined to this tract, Loasaceae, which 

 pass up the Andes to California, Larrea, Diostea, Fabiana, Pintoa, 

 Plectrocarpa, Bulnesia, Calandrinia, Tetragonia, Colletia, Discaria, 

 the phyllodineous species of Baccharis, Grahamia, Silvaea, Diposis, 

 and in bulbs Leucocoryne, Milla, Botherbe, Stephanolirion, Placea, 

 and the very peculiar tribe Gilliesieae. Northward this passes into 

 the dry tract of Central Brazil, the home of Barbacenia, Vellozia, 

 Lychnophoreae, Microlicieae, the Cassias of the Chamaecrista group, 

 and a crowd of Cactuses, erect Convolvuluses, and Mimoseae. 



The concomitants in plant form of the Hygrophilous type of con- 

 stitution are luxuriant growth, erectness, and great size of the timber 

 trees, the presence in the tropical zone of abundant climbers and 

 epiphytes, the absence of prickles, whether adventitious, or stipular, 

 or formed by indurated branchlets, leaf-borders, or calyx-teeth, the 

 absence of hair or matting from the leaves, bracts, and other foliar 

 surfaces, the abundance of flowers with large delicate corollas, and 

 the organisation of the leaves, which are planned by air- channels, 

 stomata, and the arrangement and structure of the cell-layers so as 

 to favour copious evaporation. Within the 20,000,000 square miles 

 that make up the tropical zone it is the absence and presence of 

 plants of these two opposed types of constitution that give the tone 

 to the floras. As I have already indicated which are the luxuriant 

 insular floras of the tropical zone, I need not enumerate them again. 

 Amongst the characteristic Hygrophilous types of the Tropics are the 

 woody climbers, peppers, gingers, Dracaenas, filmy ferns, Cyatheaceae, 

 Marattiaceae, Laurels, and Anonaceae. 



The distribution of Ferns in general illustrates extremely well 



