410 PHARMACEUTICAL BOTANY 



Halophytes. The plants of this group live in a soil which is rich 

 in soluble salt, usually common salt (NaCl), and on account of the 

 fact that the osmotic force of the root is nearly inadequate to over- 

 come that of the concentrated solution of the soil, the soil to such 

 plants is physiologically dry. A halophyte in fact is one form of 

 xerophyte. The most striking feature among halophytes is that 

 they are nearly all succulent plants. The leaves of such plants, for 

 example, are thick, fleshy and more or less translucent. They are 

 rich in concentrated cell sap by which they are able to counteract 

 the osmotic pull of the concentrated saline solution of the soils 

 in which they live. Anatomically they are poor in chlorophyll, 

 the intercellular-air-spaces are small and the palisade tissue is 

 more abundant. Coatings of wax are found and a hairy covering, 

 although infrequent, sometimes occurs. Coriaceous and glossy 

 leaves, especially in tropical halophytes, are noteworthy, while 

 in many salt-loving plants the stomata are sunken. Halophytes 

 are found in our coastal salt marshes and on saline tidal flats in tem- 

 perate and tropical countries and on the alkali flats of the interior 

 of continents. Notable examples of these plants are the Salt Marsh 

 Samphire, Salicornia ambigua, the Mangroves (Rhizopora) and the 

 Bald Cypress (Taxodium). 



Xerophytes. The plants of this group, like the halophytes, are 

 adjusted to live in a soil which is physiologically dry. The soil may 

 owe this condition to its physical nature, such as porosity (sand), 

 or to the presence of humic acids, or by chemical action, which in- 

 hibits the absorption of water. They are adapted to meet the con- 

 ditions of strongest transpiration and most precarious water supply. 

 To meet such conditions of physiological drought, the plants show 

 various structural adaptations. In deserts, where the atmospheric 

 precipitations are less than a certain limit, the plants acquire a 

 xerophytic structure, such as succulency, water storage tissue, 

 associated frequently with mucilage, lignified tissues, thick cuticle 

 to the leaves depressed, stomata (frequently in pits), reduced trans- 

 piration surfaces and thorns. Mechanical tissues like wood and 

 bast fibers attain their highest development in these plants. Cacti 

 and the century plant (Agave) are types of xerophytes while many 

 bog plants like the cranberry and Laborador tea, with leathery leaves, 

 are xerophytic. 



