1016 EXPERIMENT STATION RECORD. 



" Tlu* (lifloroiit aiitist'iitics diflVr in tbc inteusity of their action, but the in- 

 hibitory substance formed is jirobably the same in all cases, and also the same 

 as that formed by heat, for the quantity formed has the same effect on seeds, 

 whether produced by antiseptics or by heat. 



"On keeping; treated soils for a few weeks at a summer temperature, some 

 of the orpuiic matter which was rendered soluble becomes insoluble, and the 

 inliiliitory action is reduced. This is also the case with heated soils, especially 

 when repeatedly watered; though with unheated soils under similar conditions 

 the soluble matter increases. 



" The treatment of soils with antiseptics induces a change equivalent to that 

 obtainetl by heating the soil to 60° to 75°, and this may be sufficient to account 

 for the increased growth observed in plants grown in them. 



"The jiroduction by heat of a substance inhibitory to germination appears 

 to be a proi)erty common to all soils, twelve instances having been examined. 

 The proportion of it formed depends on the iricrease in the amount of organic 

 matter rendered soluble by heating; but the actual amount of the soluble 

 organic matter in the heated £oil is not always a criterion as to the intensity of 

 its Inhibitory action, and still less is the amount of soluble organic matter origi- 

 nally present In the unheated soil, though in the majority of cases it may be so. 

 There appears to be no connection between the fertility of a soil and the extent 

 to which it is altered by heating. 



" Soils in their natural state appear generally to contain a certain amount 

 of this inhibitory substance, as they act less favorably towards germination 

 than pure water does. Whether in any cases soils can act more favorably than 

 water — as the earlier experiments had indicated they could — is open to doubt, 

 but the probability is in favor of their doing so. So far as the instances now 

 examined are concerned, the richer soils, and those containing most soluble 

 organic matter, as slightly less favorable to germination than the poorer soils." 



The role of oxidation in soil fertility, O. Schreiner and H. S. Reed ( U. S. 

 Dcpt. Agr., Bur. t^oils Bui. 56, pp. 52). — A series of experiments is reported in 

 which the oxidizing power of roots of wheat seedlings grown in water extracts 

 of soils of different kinds was studied by means of soluble cbromogens such as 

 alpha-naphthylamin, benzidin, vanillin, vanillic acid, and esculin, which yield 

 upon oxidation by the plant roots insoluble colored compounds which are to a 

 large extent deposited upon the surface of the roots, and chromogens such as 

 phenoli)hthalein, aloin, and leucorosollc acid, which are converted into soluble 

 coloring matters in the solutions. 



The authors conclude from the results obtained in these experiments that 

 wheat roots have an extracellular oxidizing power due chiefly to the enzyms 

 which they secrete, and that oxidation is most active in the new^er regions of 

 the roots. It was found to be more pronounced in plants grown in extracts 

 of productive soils than in those grown in extracts of unproductive soils. 



" Treating the soil extracts with an absorbing agent is usually beneficial to 

 oxidation. 



" The distillate of a poor soil extract which contains volatile toxic compounds 

 was less favorable to oxidation than the residue I'emaining from distillation. 



" The process of oxidation is usually accelerated by the addition of nitrates 

 to an aqueous soil extract. The addition of ammonium sulphate is less bene- 

 ficial to oxidation than the addition of an equal amount of nitrogen in the 

 form of nitrate. 



" Calcium salts were found to increase the amount of oxidation in cultures 

 to which they were added. 



" The addition of potassium salts was not generally beneficial to the proc- 

 esses of oxidation. In some cases their presence caused a material retardation 



