186 CHARACTERISTICS OF THE ZONES OF MOISTURE. 



The large floras of decidedly Xerophilous type are five in number, 

 two in the Northern and three in the Southern JSiemisphere, and are as 

 follows : — 



1. The Desert flora, extending from the Canaries through the 

 Sahara, through Egypt and Arabia, to the Indus delta. This is not 

 so rich in large groups of decidedly Xerophilous type as some of the 

 others, but it is the largest arid tract in the world, and has a great 

 many endemic genera and species. In the Canaries we have Ironiura, 

 vEonium, Greenovia, Monanthes, ITleinia, Ceropegia,' and Euphorbia 

 canariensis. In the Continental portion of its area there occur several 

 Cactus-like Euphorbias, a few Stapelias and Mesembryanthemums, 

 Aloe Socotrina, Eetama, Boswellia, Balsamodendron, Nitraria, 

 Sectzenia, Miltianthus, Reaumuria, Anastatica, many erect shrubby 

 Convolvuluses and prickly Acacias, Prosopis, Maerua, Sphcerocoma, 

 Fagonia, Balanites, FranccBuria, Peganum, Crotalaria arenaria and 

 thebaica ; and amongst bulbs, Ornithogalums, Scillas, Urgineas, 

 Xiphions, Trichonemas, Erythrostictus, and Dipcadi serotinum. This 

 passes at its oriental extremity into the little-known flora of the 

 Tibetian plateau and the heart of Asia, the great home of Astragalus, 

 Allium, Artemisia, Calligonum, Halimodendron, Galatella, and Cou- 

 einia ; but it is completely broken up and dissipated in the eastern 

 half of Asia by the Himalayas, and does not penetrate into China. 



2. The flora of Southern California, New Mexico, Texas, and 

 North Mexico, running out north to Utah and Kansas, but stopped 

 in a southern direction by the Mexican Andes. This is the exclusive 

 liome of Agave and its allies Beschorneria and Fourcroya, of the 

 rigid-leaved tree Liliacete, Yucca, Hesperaloe, Dasylirion, and Beau- 

 carnea, and is the great centre of the Cactuses. Of other Xerophilous 

 types it possesses Dion, Echeveria, Claytonia, Spragaea, Taliuum, 

 Lewisia, Larrea, Eriogonum, many spiny Mimosece, many fleshy- 

 leaved Portulacese and Chenopodiaceas ; and in bulbs Calochortus, 

 Milla, Tigridia, Bigidella, Ferraria, and several Alliums, Bessera, 

 and Androstephium. 



3. The flora of Southern Angola, stretching down to the coast to 

 the mouth of the Orange River, and across the Kalihari Desert and 

 Cape Karroo to Kaffir-land. This is the great home of Aloe (of which 

 one huge arborescent species is said to reach 150 feet in the spread 

 of its branches), Gasteria, Haworthia, Stapelia, and Mcsembryanthe- 

 mum, of which latter alone there are said to be three or four hundred 

 species of extremely varied habit; and of the cactus-like Euphorbias. 

 This the richest Xerophilous flora in the world, and amongst many 

 other striking types possess Kalanchoe, Cotyledon, Portulacaria, 

 Rhipsalis, Bulbine, a great variety of Crassulas, Welwitschia, 

 Acanthosicyos, Encephalartos, Prionium, Augea, Sisyndite, Sarco- 

 caulon, a great number of Helichrysa, Vitis Macropus and Bainesii, 

 Anacampseros, many tuberous-rooted Pelargonia, Oxalises and Ascle- 

 piads, Kleinia, Othonna, Adenium, Pachypodium, Testudinaria ; in 

 rigid and dotted-leaved shrubs crowds of Proteaceae, Diosmece, Clif- 

 fortia, Cluytia, and the Karroo genera of Compositae, and iu bulbs 

 Massonia, Lachenalia, Drimia, Ixia, Gladiolus, Babiaua, Tritonia, 

 Moraea. Androcymbium, and the curious climber Bowiea. 



4. The flora of Central Australia, including the Swan River terri- 



