ECOLOGY 



145 



deserts. The stem may be thickened and full of water; a covering of hairs 

 or some other covering may occur and lessen loss of moisture by evapora- 

 tion. Examples of xerophytes are the cacti, yuccas, agaves, etc. 



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Xerophytic conditions. A typical desert. 



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

 lives contains salts, such as sea salt or the al|<:ali salts of some of 

 our Western lakes, then the conditions are said to be halopJiytic, 

 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 

 amount of water in the soil and air surrounding them. Such are 

 most of our forest and fruit trees, and many of our garden vege- 

 tables. Conditions of moderate moisture are called mesopJujtic ; 

 the plants living thus are known as mesophytes. 



It may easily be seen that plants which are mesophytes at one 

 time may under some conditions of weather be forced to undergo 

 xerophytic or hydrophytic conditions. An oak tree may receive 

 no water through the roots during the winter because the surface 



hunter's BIOL. — 10 



