32 Harshbcrger — Water Storage and Conduction in 



which alone are able to grow under such sterile conditions. 

 One of these plants in particular, gives character to the larger 

 vegetation, and is a conspicuous object on all of the drier 

 ledges. The stem has an upright habit with tufted leaves at 

 the top of a bright green color, and it can be seen for a con- 

 siderable distance, as a prominent object on the lava bed. 



It resembles several of the endemic plants of the Canaiy 

 Islands. In the zone of succulents, on these islands, grow 

 plants which have adapted themselves to the long dry season.* 

 A typical collection of these plants in the geographic arrange- 

 ment of the Berlin Botanic Garden, so struck the writer as to 

 their resemblance to Senecio prcBcox, that the following list was 

 made of the Canary succulents found there. The most note- 

 worthy examples are the following: Eiiplwrbia canariensis, 

 E. inauritanica, Sempcrvivuin strepsicladum, S. tirbicum, S. arbor- 

 etmi, S. Iwlochrysiini, S. Youngiamun, Senecio antenphorbinm 

 and vS. Kleinia. The Canarian species of Settecio (which are 

 found on geologic formations entirely volcanic, as evidenced 

 by the traces of former seismic activity, the exceedingly 

 mountainous, broken and jagged nature of the land)t are 

 remarkably similar in habit and appearance to Senecio prcBcox 

 of the Valley of Mexico. Similar conditions of environment 

 physiologically affect plants of the same, and even of widely 

 divergent, genera in an identical manner. 



Many other plants are known, which give character to par- 

 ticular portions of the earth's surface. Cereus giganteus is found 

 in Arizona ; along the tidewater strands of the tropical seas 

 the mangrove is predominant ; in the Floridan swamps, the 

 bald cypress grows ; on the deserts of the Mexican plateau, 

 tree yuccas, and cacti abound ; in the Kalahari Desert of South 

 Africa, Welwitschia mirabilis {Tuniboa Bainesii) grows ; in 



*Grisebach. — " Die Vegetation der Erde," ii, p. 482-88, 1884. 

 *Drude. — " Handbuch der Pflanzengeographie," p. 393-94, 1S90. 

 t Alice C. Cook. — "A Sketch of the Flora of the Canary Islands." " Bulletin, 

 Torrey Botanical Club," xxv, p. 351, 1898. 



