8 



iug point occuiTed included only fifty-four days, and the 

 thermograph recorded freezing temperatures on but fifty days 

 of this time. After the above date the rise was steady and 

 continuous with minor fluctuations. 



I.V. Vr'V£^"g' ^^ ■ Sept- 1^ [gPJ- 



Fig. 4. — Tracings of thermograpliic curves of the air, and of tlie soil 

 at a deptli of 30 centimeters (1 foot), August 4-September 1, 1902. A 

 period during which comparatively little fluctuation and variation occurs. 

 Centigrade scale. The temperature of the air is shown by the uppermost 

 of each pair of tracings. 



Both the maxima and minima are higher in January than in 

 December and are still higher in February, at which time the 

 temperature of the air reaches its annual minimum. As a con- 

 sequence of the above conditions the roots of plants at a depth 

 of a foot (30 centimeters) in this locality find increasingly 

 more favorable conditions for activity after the latter part of 

 December. Growth and division of the cells, and the attend- 

 ant respiration would ensue in man}- species at an accelerated 

 rate over that prevalent in the earlier mouths of the winter 

 and the absorjDtion of mineral and other compounds could take 

 place to the utmost capacity of the plant. This will still be 

 more apj^arent when it is seen that the temperature of the soil 

 at a depth of a foot is but little lower in February than it is 

 in April or May at a time when the growth and formation of 



