XEROPHYTES AXD 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) 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. 



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 . 36g ._ A plant of houseleek ^ fmpervivum 



in the well-known " "^- tect<n "') showing fleshy leaves arranged in a 



plant,' on which 

 hairs glisten like ice. 



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

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

 large and thin-walled, as in begonias, figs, and peppers (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 



rosette, with offsets formed at the ends of speciai 

 branches. These become detached and form in- 

 dependent plants. About one half natural size. 

 After Gray. 



