SOIL TEMPERATURE FACTOR IN ROOT GROWTH 07 



sufficient root growth to bring about the estabhshnient of the 

 species. In this connection favorable moisture relations and 

 favorable soil aeration are assumed. 



It may emphasize the really great difference in the effective- 

 ness of the temperature of the soil at Carmel and at Tucson, 

 so far as the influence on root growth of Covillea is concerned, if 

 we compare the TR of each to what might be expected if every 

 hour of the month were at the optimum temperature and if the 

 maximum rate of root growth were maintained throughout 

 that period. Under such circumstances the root growth would 

 be 1190 cm. It is thus seen that at Carmel in August the growth 

 under actual conditions could not be over one-sixteenth the 

 maximum at the optimal temperature, while that at Tucson 

 would be approximately one-half the maximum. Therefore, if 

 a numerical expression of the relative intensity of the effective- 

 ness of temperature conditions at a depth of 30 cm. at the two 

 stations is desirable, it can be said that the effectiveness of the 

 soil temperatures at Tucson in August are approximately eight 

 times that of the temperatures of the soil at the same depth and 

 at the same time at Carmel. 



