growing season, and if these roots reach the permanent under- 

 ground water supply, further growth of the plant is not directly 

 dependent on local rainfall. However, most seedlings produced 

 by phreatophytes are not successful in reaching ground water 

 supplies and as a consequence seedling mortality is generally 

 very high. 



Xerophytes include succulents, which are plants such as vari- 

 ous cacti or members of other families having fleshy stems and 

 leaves that enable them to store water for long periods of time. 

 Succulent xerophytes frequently have shallow root systems and 

 thus are able to utilize the soil moisture that results from a light 

 rainfall or from heavy dew. Such plants take advantage of what 

 little precipitation falls in desert regions and store this water for 

 months or years, during which time it is slowly and economically 

 used in the metabolism of the plant. Many succulents, such as 

 most cacti, are leafless and are so shaped that they present a 

 minimum surface area from which water loss can occur. 



Non-succulent xerophytes, such as some species of the sage- 

 brush genus Artemisia (Compositae), Creosote Bush, and Ocotil- 

 lo, have developed various means other than water storage in 

 succulent tissue to endure long periods of drought. The means by 

 which xerophytes deal with the scarce water supply vary. Some 

 of these plants are able to obtain water from the soil even when 

 it is present in very low amounts, because they have a high diffu- 

 sion pressure deficit within their root cells, thus enabling the 

 roots to take up what little water is present in the soil long after 

 rains have fallen. Many of these xerophytes have developed com- 

 binations of other characteristics which enable them to econo- 

 mize on water. These include the presence of a heavy waxy 

 cuticle on the leaves and stems which reduces water loss from 

 these tissues; presence of dense mats of hairs, which have the 

 same function; vertical orientation of leaves which places the 

 leaves at such an angle that they receive the full sunlight obliquely 

 rather than directly, and thus do not become heated; grayish 

 color of leaves and stems due to pigmentation, waxes, or hairs 

 wdiich also reduces heating-up of plant tissues; leaves curling (or 

 dropping) during drought periods to reduce the surface area from 

 which water loss may occur; sunken stomates (pores) on the 



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