326 



PLANT LIFE. 



upper to the lower side of the leaf may act as reservoirs 



of water. 



442. 3. Tubers and bulbs. — These forms of the shoot 

 A. /f in which the parenchyma is 



abundant and richly supplied 

 with water may also be 

 counted, in part at least, as an 

 adaptation for water-storage. 

 443. III. Halophytes. — 

 The salt-loving plants are, 

 in most of their characters, 

 strikingly similar to the xero- 

 phytes. This similarity is to 

 be explained probably by the 

 difficulty of securing a suita- 

 ble water supply. They grow 

 near the ocean, upon the 

 shores of salt lakes, by salt 

 springs, and in the interior 

 of the great continents in old 

 lake basins in which the salts 

 have accumulated by the 

 rains. A few of the halophytes 

 are trees and shrubs, with 

 leathery leaves, but almost all 

 are succulents. In habit they 

 are generally low, often creep- 

 ing, with thick, fleshy and 

 more or less translucent leaves 

 and stems ; the cells large and 

 thin-walled, containing com- 



Fig. 370.— Strip from a vertical section of 

 leaf of Pefieromia trichocarpa. A, from 

 a fresh leaf ; iu, water-storing tissue, com- 

 posed of the multiple epidermis of the 

 upper side ; a, chlorophyll-bearing cells ; 

 s, spongy parenchyma with sparse chloro- 

 plasts and much water. />', the same after 

 four days' transpiration at 18-20 C. The 

 tissue w is much collapsed, the walls being 

 plaited; j also shrunken, but a as before. 

 Magnified about 50 diam. — After Haber- 

 landt. 



paratively little chlorophyll and abundantly supplied with 

 water, with few and small intercellular spaces and the surface 

 generally smooth. 



