11 



of no more than 50 centimeters (20 inches) may be traversed, 

 occui)yin^- a matter of a few minutes, or an hour at most, 

 during which time the tem])erature is raised the al)Ove amount. 

 The warming of tlie licjuid as it passes upward tlirough tlie 

 living and nonliving cells is attended by alterations in its 

 solubility of mineral and organic substances and by a de- 

 creased capacity for holding gases in solution. The down- 

 Avard movement of solutions of sugars, acids, and nitrogenous 





"X TmH^uVv^\huvU»^:icrDec . 's^gg/^goa.p 



Fig. 7. — Tracings of thermographic curves of air, and of the soil at a 

 depth of 30 centimeters ( 1 foot), November 3-December 1.'), 1002. The 

 soil romaiued below the freezing point until December 8, when it began 

 to rise steadily, and did not fall below freezing point during the re- 

 mainder of the winter. Centigrade .scale. The temperature of the air 

 is shown by the uppermost of each pair of tracings. 



