leaves to reduce water loss; and wide spacing of plants, perhaps 

 in response to the low water supply. Further, a variety of thorns, 

 spines, or essential oils may serve to discourage browsing animals 

 from eating the leaves and stems of xerophytic plants. 



E CO types and Life Zones 



Many wide-ranging species of plants are variable throughout 

 their range. This variability may be expressed in morphological 

 characteristics such as height of plant or size of leaves; in "be- 

 havioral" characters such as time of flowering or season of leaf 

 fall; or in subtle physiological characters such as tolerance to 

 specific soil conditions, such as serpentine soil. Some environ- 

 mental characters, soil type, for example, show a discontinuous 

 distribution, and plants respond accordingly. However, one im- 

 portant environmental feature >\diich shows a graded variation 

 is that complex of phenomena which we collectively call climate. 

 Climatic factors such as average rainfall, average temperature, etc., 

 tend to show rather gradual changes from one area to the next. 

 The difference in the average annual climate between a locaUty 

 at 3,000 feet (914 m) in the Sierra Nevada or San Gabriel Moun- 

 tains and one at 4,000 feet (1 ,219 m) in the same mountains is 

 very slight. The difference between 3,000 and 5,000 feet (914 

 and 1,524 m) is stronger. Obviously the difference between the 

 average climate at sea level in coastal California and the top of 

 Mount Dana in the Sierra Nevada or Mount San Jacinto in south- 

 ern CaUfomia is very great. Few plant species occupy such a 

 diversity of habitats, but there are a few plant species in Califor- 

 nia which are widely distributed and occur in a variety of climatic 

 regimes. In view of the interesting adaptations demonstrated by 

 soil ecotypes of such species as Gilia capitata, what adaptations 

 to climatic differences can we expect in a climatically diverse 

 plant species which occurs in a wide variety of habitats in 

 California? 



The Carnegie Group 



In the 1930's, a trio of botanists in California began a long 

 series of investigations aimed at answering the question posed 

 above. Their results were pubUshed primarily in a monographic 



47 



