ROOT GROWTH AND TEMPERATURE 



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experiment was 3.8 to 5.8 mm. In the experiment with the 

 shorter roots the rate of growth increased during the first 45 

 hours or more, and then declined or remained approximately 

 constant. In the experiment with the longer roots the rate 

 of growth increased up to 30 hours, more or less, when it de- 

 creased or remained aboiit constant. 



Fig. 1. Root growth of mesquite seedling, experiment VII, plant no. 46. 

 Temperature of soil,31.5°C. The initial root length was 16 mm. Readings every 

 three hours. Growth X 15. 



Fig. 2. Root growth of mesquite seedling, experiment IV, plant no. 26, tem- 

 perature of soil 28.5°C. Initial length of root was .38 mm. Readings at inter- 

 vals of three hours. Growth X .30. 



A comparison of the character of curves made from the two 

 groups of measurements indicates that the crest of the curve 

 was reached sooner in the longer roots than in the shorter ones, 

 and also that the growth rate varied more from reading to read- 

 ing — at 3 hour intervals — in the shorter than in the longer roots. 



Root growth at a soil temperature of 30. 5° C. The initial 

 length of the roots in the experiment at a soil temperature of 

 30.5°C., was between 41 and 62 mm. In each instance the rate 



