I9I2] Fred J. Scaver and Ernest D. Clark 423 



source of this material it seems to show properties of sugars and 

 also of organic acids. The cellulose or humus substance seems to 

 be changed by the heat into a series of decomposition products 

 having the groups characteristic of sugars and also of organic acids. 

 Precipitation with normal lead acetate and then with the correspond- 

 ing basic salt produces a partial Separation of these substances, as 

 also does the addition of acetone. The relation of this organic 

 material to the constituents of caramelized sugar would make an 

 interesting study. 



CROP EXPERIMENTS 



Many experiments with the fungus Pyronema had shown that 

 the stronger the extracts of heated soils the better media they were 

 for this fungus. Other authors had reported that the green plants 

 did not take kindly to soils which had been heated to a high tempera- 

 ture. From the above observations it occurred to us that the harm- 

 ful effects from the heating of the soil in which certain plants are 

 grown might not be due to the fact that the materials rendered 

 available by heating are especially harmful, but that they are formed 

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

 This view is strengthened by the experience of Livingston^^ and 

 others that growth is accelerated in weak Solutions and retarded in 

 concentrated ones. On the other band, the lower plants such as 

 yeast and fungi are able to grow in Solutions that would very rap- 

 idly plasmolyze the cells of the higher plants.^^ Evidently, then, 

 the osmotic pressure of their cells must be in equilibrium with that 

 of their medium. In order to test this conception as applied to our 

 problem it was decided to try the effect of the growth of a given 

 plant on the same kind of soil heated to different temperatures. In 

 looking about for a plant to be used in these preliminary experi- 

 ments, the common oat (Avena sativa) was selected for the reason 

 that it had been previously observed that the burning over of the sur- 

 face of the soil seemed to accelerate the growth of this particular crop. 



^ Livingston : The role of diffusion and osmotic pressure in plants, pp. 124- 

 144. 1903. 



"This matter is discussed in Jost's (Gibson translation) Plant Physiology, 

 p. 179- 1907. 



