I9I2] Fred J. Seaver and Ernest D. Clark 427 



SUMMARY OF CONCLUSIONS 



1. The color of the extracts of heated soils varies with the tem- 

 peratures to which the soils have been subjected; the extract of 

 unheated soil being colorless, that of soil heated at 90° C. being 

 shghtly yellowish, that of soil heated at 120° C. being more deeply 

 colored. 



2. The amount of soluble matter in the soil also varies with the 

 temperature to which the soil has been exposed and to this the color 

 of the extracts serves as an index; the deeper the color the more 

 soluble matter the extracts contain. 



3. The length of time during which the soil has been exposed 

 seems to be of little moment; soil heated at 120° C. for ten hours 

 containing little more soluble matter than the same soil heated at the 

 same temperature for only two hours. 



4. Growth of the green plants used by us is slightly accelerated 

 in soils heated at low temperatures (90-120° C.) but above this 

 point growth is retarded, the retardation increasing with the tem- 

 perature to which the soils have been exposed. 



5. Retardation seems not to be due to the toxic effects of the 

 substances rendered soluble, but to the fact that they are present 

 in such large quantities that the plant is unable to absorb them. 



6. The influence of heated soils on the growth of fiingi is the 

 opposite of that on the growth of green plants, the growth becom- 

 ing more luxuriant as the temperature is increased. This can be 

 explained by the fact that fungi, unlike most green plants, have the 

 power of adapting themselves to nutrient media of a comparatively 

 high degree of concentration. 



7. The beneficial or harmful results, therefore, of the heating of 

 a soil for the growth of plants, depends upon the temperature to 

 which the soil has been heated as well as upon the nature of the 

 soil and the plant. 



8. The preference of certain plants for burned-over areas or 

 for peaty soils may be explained by the acidity of such situations, 

 a supposition we are testing by blueberry culture experiments now 

 under way. 



Finally, we wish to express our thanks to Professor William J. 

 Gies for his helpful suggestions during the course of our inves- 

 tigations. 



