XEROPHYTES AA'D HALOPHYTES. 325 



C. Adaptations for storing water. 



440. I . Special cell contents. — The simplest of these adap- 

 tations is the presence of mucilage in the cells, arising from 

 the cell-wall or developed in the cell-sap of various parts. 

 (See *\ 5.) The presence of acids, tannins, and salts perhaps 

 aids in the retention of water. 



441. 2. Water-storing tissues. — {a) Flesliy plants, or 

 succulents, are those which thicken their parts by the develop)- 

 ment of an unusual amount of parcnch\nia, which contains 

 a large quantity of cell-sap, and usually much mucilage. 

 These thin-walled, mucilage-containing tissues form a reser- 

 voir for the storing of water. In such ]olants the epidermis 

 is very strongly water-proofed; the stems are thick, cylin- 

 drical, prismatic or spheroidal ; tlie lea\es are wanting, or they 

 are thick and llesh)-, cylindrical or broad (fig. 369), and 

 arranged in rosettes. 



(li) In non-succulents, 

 the epidermis itself may 

 be greatly developjed as 

 a water-storing tissue, 

 or it nray form great 

 numbers of bladdery 

 hairs which are richly ' 

 supplied with water, as fig. 369.-A '^^tZ^^^'vysLfcrvivum 



I'n t-lnp ivpU l-nnwii " i,-.= tictorum'). showin.s fleshy leaves aiTanged in a 



m tne \\ en-knO'\\ n ice- rosette, with offsets fonned at the ends of special 



TlTi-if '' -,,-, n-Vii'/l-. fVi^ brandies. Tliese lieconie detached and form in- 



piauc, on WlilCll me dependent plants. About one half natural size.— 



1 ■ 1 ■ i. 1 ■ 1 • After tirav. 



nairs glisten like ice. 



In the first case, the epidermis, instead of forming a single 

 layer of cells, may develop into several lavers, the lower ones 

 large and thin-walled, as in begonias, figs, and pcpipers (fig. 

 370). The cells immediately under the epidermis sometimes 

 become transformed into a water-storing ti.ssue, as in the 

 oleanders (fig. 36S); or strips of tissue extending from the 



