9 



new organs in the shoot is jit a iiiuxiniiiin. The jipproiich of 

 the sprinp: season in this locality therefore finds the root sys- 

 tems and absorbing organs of the vegetation which pene- 

 trates the soil to the given depth in a state of comi)aratively 



Fig. 5.— Tracings of thermographic curves of the air, aud of tiie soil 

 at a depth of 30 centimeters (1 foot), September 1-29, 1902. A general 

 decrease in the temperature of the soil amounting to about 5° C. was 

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

 uppermost of each pair of tracings. 



great activity, and it needs but the exposure of a few days or 

 even of a few hours in some plants to alloAv for very marked 

 development of the stems, leaves, and flowers. 



Another i:)oint of interest in the present connection is the 

 fact that such notable differences are found between the temp- 

 eratures of the subterranean and aerial portions of the bodies 

 of plants at almost all seasons. During June, 11)02, the shoots 

 of herbaceous plants were in an atmosphere that varied be- 

 tween 8° C. (46.5° F.) and 34° C. (92.5° F.), while the roots 

 were between 8° C. (46.4° F.) and 18° C. (55.4° F.). As the 

 maxima and minima were not synchi'onous the actual differ- 

 ence between the temperature of twigs and leaves on the up- 

 per part of the plant, and roots on the lower amounted to as 



