38 Harshberger—Water Storage and Conduction in 
tion, and the vessels which have to supply the leaves must 
make up the deficiency by receiving water from below. 
An examination of Plate VIII, Fig.1, will show the appear- 
ance of the pith discs as they occur in the turgescent condition. 
That it takes but a short time to refill the emptied discs was 
demonstrated by placing pieces of dry stem (Figs. 2a and 2 b) 
in water. At the end of twenty-four hours, the dry mem- 
brane-like discs of the medulla imbibed water and swelled 
to about their original size as in Fig. 1. It would, therefore, 
appear that a single heavy rain would be sufficient to replenish 
the water, which it takes the plant months, or even a year, to 
consume. 
Ludwig * in giving a résumé of our knowledge of xerophytes 
says: ‘Eine Anpassung an die trockensten Wohngebiete 
(mit oft 34 Jahr lang anhaltender Trockenheit, stellen die 
Fettpflanzen oder Succulenten dar, bei denen durch besondere 
wasserspeichernde Gewebe das Wasser wahrend der kurzen 
nassen Jahreszeit in grosserer Menge aufgesammelt und bis 
zur nachsten Nasseperiode angesammelt wird. Man hat diese 
Gewachse verglichen mit dem ‘Schiff der Wiuiste,’ dem 
Kameel.”” Professor Warming f gives us an instructive classifi- 
cation of water storing cells and tissues in a large number of 
plants, but in no place does he lay especial emphasis on the 
pith as a storage centre. Henslowf{ speaks of the pith with- 
out examples being given. He says: “In stems, the cortex 
and medulla act as storage tissue.” Goebel,§ referring to 
succulent plants in general, makes this statement with reference 
to Kleinia articulata, a composite plant, where water is stored 
up in the pith: ‘“‘ Das Wasser ist theils im saftigen Rinden- 
gewebe, teils im Marke enthalten (letzeres z. B. sehr auffallend 
* Lupwic.—‘‘ Lehrbuch der Biologie der Pflanzen,’’ p. 177, 1895. 
+WARMING.—KNOBLAUCH, “‘ Lehrbuch der cekologischen Pflanzengeographie,”’ 
p- 199, 1896. 
} Henstow.—“ Origin of Piant Structures,”’ p. 77, 1895. 
2 GOEBEL.—Pflanzenbiologische Schilderungen,’’ I, p. 54, Fig. 24, p. 55, 
1889. 
