PLANTS MODIFIED BY THEIR SURROUNDINGS 161 



appearance of a cactus under desert conditions. Thus they lose 

 their evaporating leaf surface by having the leaves changed into 

 spines. 



The stem may be thickened so as to store water ; a covering of 

 hairs or some other material may be present and lessen loss of 



Xerophytic conditions. A typical desert. 



moisture by evaporation. The conditions of extreme dryness 

 under which such plants live is called xerophytic, and such 

 plants are known as xerophytes. Examples of xerophytes are 

 the cacti, yuccas, agaves, etc. 



Halophytes. — If the water or saturated soil in which the plant lives 

 contains salts, such as sea salt or the alkali salts of some of our Western 

 lakes, then the conditions are said to be halophytic, and a plant living 

 under such conditions is known as a halophyte. 



Halophytes show many characteristics which xerophytes show, spines 

 or hairs, thick epidermis, fleshy leaves, all being characters which show 

 that the water supply of the plant is limited. The density of the salt 

 water in the soil makes it difficult for the plant to absorb water ; hence 

 these characters are developed. 



Mesophytes. — Most plants in the Temperate Zone occupy a 

 place midway between the xerophytes on one hand and hydro- 

 phytes on the other. They are plants which require a moderate 



HUNT. ES. BIO. 11 



