38 Harshberger — Water Storage atid 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. i, 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. 2 a 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. i. 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 resume of our knowledge ofxerophytes 

 says : " Eine Anpassung an die trockensten Wohngebiete 

 (mit oft y^ 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 Wiiste,' 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. Henslow| 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 Kleiuia 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 



* Ludwig. — " Lehrbuch der Biologic der Pflanzen," p. 177, 1895. 



f Warming. — Knoblauch," Lehrbuch der oekologischen Pflan/engeographie," 

 p. 199, 1896. 



:j: Henslow. — "Origin of Plant Structures," p. 77, 1895. 



I GoEBEL. — Pflanzenbiologische Schilderungen," I, p. 54> Fig. 24, p. 55, 

 1889. 



