XEROPHYTES AND HALOPH YTES. 325 



C. Adaptations for storing water. 



440. 1 . 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 *j" 5.) The presence of acids, tannins, and salts perhaps 

 aids in the retention of water. 



441. 2. Water-storing tissues. — (a) Fleshy plants, or 

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

 ment of an unusual amount of parenchyma, 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 plants the epidermis 

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

 drical, prismatic or spheroidal ; the leaves are wanting, or they 

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

 arranged in rosettes. 



(U) In non-succulents, 

 the epidermis itself may 

 be greatly developed as 

 a water-storing tissue, 

 or it may form great 

 numbers of bladdery 

 hairs which are richly 



supplied with water, as FlG , 3 , 9 ._ A 3Trfto«£k \sL* 

 in the well-known "ice- ^SVSSSPfoKS 5*?e3KF 



,i„„, •• ._ ,,.i,;,.k ,k., branches, these become detached and form in- 

 piam, on \\nun lilt, dependent plants. About one half natural size.— 



hairs glisten like ice. After Gray. 



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

 layer of cells, ma) develop into several layers, the lower ones 

 large and thin-walled, as in begonias, figs, and peppers I fig. 

 370). The cells immediately under the epidermis sometimes 

 become transformed into a water-storing tissue, as in the 

 oleanders (fig. 368); or strips of tissue extending from the 



