It is necessary to scratch the coat of these seeds in order for ger- 

 mination to occur, otherwise they are impervious to water. The 

 grinding action of sand and rocks in the flash floods of the desert 

 performs the scarification function and also provides the seedHngs 

 with abundant water which will supply their requirements during 

 the first few weeks of growth. Such floods also serve to disperse 

 the seeds. Like many desert perennials, seedlings of wash wood- 

 land trees produce only two or three leaves immediately after 

 germination and then seemingly become dormant. However, these 

 plants are far from dormant during this time, but are devoting 

 their chief energies to developing extensive, deep root systems 

 that will enable them to survive long after the moisture from the 

 flood has dissipated. 



Summer temperatures in the Creosote Bush Scrub may be very 

 high, and in many areas winter temperatures do not drop to the 

 freezing point. The average annual rainfall in this plant commu- 

 nity is very low, ranging from 2 to 8 inches (5 to 20 cm). In ap- 

 pearance. Creosote Bush Scrub is composed of numerous shrubs 

 or small trees to 10 feet (3 m) high or somewhat higher, that are 

 widely and symmetrically spaced. Some of these species, parti- 

 cularly those that occur along the desert washes, are very colorful 

 when in flower. 



The Creosote Bush Scrub is dominated by woody plants, but 

 it is also a plant community in which there is a rich representation 

 of annual plant species (Plate 16C). In addition, herbaceous 

 perennials also are present although they are less abundant than 

 are herbaceous annuals. The general vegetational aspect of the 

 Creosote Bush Scrub during almost any month of the year belies 

 its arid nature. It is usually green and, since it supports a cover of 

 shrubs and small trees, it may give the impression that it receives 

 more rain than it actually does. 



113 



