206 Studies of Plant Growth in Heated Soil [Jan. 



From the work of Seaver and Clark it appears that the materials 

 rendered soluble by subjecting soil to dry heat show properties of 

 sugars and organic acids ; others have obtained results suggestive of 

 soils composed almost entirely of humus, the acid nature of which 

 is well known. It is possible that the preference of certain plants 

 for peaty soils or burned-over areas may be due to the acidity of 

 these soil types. Certain facts observed by the present writer in 

 the course of the experiments described above, as well as field obser- 

 vations on the same crops in swamp soils which were very rich in 

 humus, appear to bear out this theory. Buckwheat is usually grown 

 on poor soil, where it thrives. The writer has seen a number of 

 attempts to grow it on swamp land with uniformly unsatisfactory 

 results. Comparable to this is the effect of subjecting the soil to a 

 very high temperature. Wheat is also usually grown on a loamy 

 soil of a rather low humus content as compared with swamp lands. 

 When grown on the latter it has a tendency to produce weak stems 

 with a consequent "lodging" of the grain. This is at least true in 

 regard to certain varieties. The behavior of the plants on the soils 

 which had been subjected to the higher temperatures suggests anal- 

 ogous results, as the leaves were flaccid and lacking in normal 

 rigidity. 



Throughout the entire series of experiments delayed germina- 

 tion and retarded growth characterized all the crops grown on soil 

 subjected to a temperature of 175 . These results were quite 

 marked. Similar results, but in a less pronounced degree, were 

 noted in cultures on soil heated to 135 . Not only was the growth 

 of these plants retarded, but their susceptibility to disease was 

 increased. 



The writer's experiments agree with those of Seaver and Clark 

 in indicating that soils subjected to a low degree of heat (120 C, 

 or less) show an accelerated growth of green plants and a retarda- 

 tion of fungous growth, while soils heated to a higher temperature 

 give results which are the reverse, i. c, retarded growth of green 

 plants and accelerated growth of fungi. These results also accord 

 in the main with more recently published results obtained by other 

 workers, although on the surface some of these may appear to differ. 



