HEATED AND TREATED SOILS 251 



which could be applied before the heated soils had had time to 

 alter their character to any appreciable extent, and also that 

 the results of germination are not complicated by bacterial 

 changes in the soil, germination being independent, as was 

 proved, of the presence or absence of bacteria. 



The results of this examination were to show that the sub- 

 stances rendered soluble in soils by heating, act as toxins towards 

 germinating seeds, not only retarding their germination, but 

 reducing the number of seeds which eventually germinate (IX, 

 Appendix, p. ix), and that this action gradually disappears 

 with the disappearance of the excess of soluble matter when 

 the heated soils are kept for any length of time exposed 



, o 



Organic Matter 



Ti me 

 200 



Incubation Tirrves 



(OO 



50 IOO 



Temperature o~f Heating. 



FIG. 25. RELATION BETWEEN TEMPERATURE, ORGANIC 

 MATTER AND INCUBATION. 



to atmospheric influences. The drawings in Fig. 25 (XII, 

 Appendix, pp. 271 and ii) show the relative values obtained with 

 heated soil, as compared with that obtained with unheated soil 

 represented as 100 ; the curves in the upper portion refer to the 

 soluble organic matter present o, 44 and 112 days after the heat- 

 ing; whilst those in the lower portion refer to the incubation 

 times of the seeds when they germinate in these same soils. 

 The general connection between the two sets of phenomena is 

 obvious, though the proportionality between them is not a 

 direct proportion, since the upper figure represents the cube 

 root of the percentages of soluble matter, whereas the lower 

 figure represents the actual incubation periods ; also it will be 

 seen that, when the incubation times of seeds in heated soils 

 become reduced nearly to their original value, as happens after 

 160 days, there still remains in the soil a considerable portion 



