26 



PLANT HABITS AND HABITATS IN THE 



recorded for 30 cm. depth was 99° F. (37.22° C.) and the minimum 

 was 44° F. (6.67° C). The yearly course of the soil-temperatures for 

 this depth is as follows: Beginning with high temperatures of late 

 summer, just before the rains, the temperature drops with the rains 

 and continues the downward movement until March, when a fairly 

 rapid rise begins and persists until the rains of midsummer. 



Additional records of 60 cm. and 120 cm. depths, unpublished, show 

 noteworthy features, some of which are as follows : In neither case is 

 there a daily variation determinable by the apparatus employed. In 

 both of the greater depths the maximum temperatures are attained 

 (as at the two lesser depths) just before the rains of midsumm:r. At 

 a depth of 60 cm. the maximum temperature observed was 89° F. 

 (31.67° C.) and at a depth of 120 cm. the maximum was 79° F. 

 (26.11° C). The minimum temperature at a depth of 120 cm. was 

 56° F. (13.33° C), and the annual range was observed to be 24° F. 

 The course of the temperature at this depth following the rains of 

 summer is downward until late in winter, when it gradually rises until 

 midsummer. Thus the quick temperature rise in spring characteristic 

 of the soil at a depth of 15 cm. does not occur at the greater depths. 



The soil of which the temperature at a depth of 15 cm. and 30 cm. 

 was reported on in the preceding paragraph is an adobe clay, and 

 that of which the temperature at greater depths was characterized 



Fig. 8a. — Mean annual evaporation in Australia, after Hunt. 



