a2 Harshberger—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 Canary 
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 precox, that the following list was 
made of the Canary succulents found there. The most note- 
worthy examples are the following: Luphorbia canariensis, 
E. mauritanica, Sempervivuim strepsicladum, S. urbicum, S. arbor- 
eum, S. holochrysum, S. Youngianum, Senecio anteuphorbium 
and S. Kleinia. The Canarian species of Senecio (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) are 
remarkably similar in habit and appearance to Senecto precoxr 
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 (Tumboa Baines) grows; in 
* GRISEBACH.—‘‘ Die Vegetation der Erde,”’ ii, p. 482-88, 1884. 
* DrupE.—‘‘ Handbuch der Pflanzengeographie,”’ p. 393-94, 1890. 
+ ALICE C. Coox.—‘‘A Sketch of the Flora of the Canary Islands.’’ ‘ Bulletin, 
Torrey Botanical Club,” xxv, p. 351, 1898. 
