When soils are treated with antiseptics, such as carbon disulphide, chloroform, benzene, ether or paraffin oil, they undergo chemical change, and the soluble organic matter in them is increased, just as in case of their being heated; they also exhibit the same inhibitory effect on the germination of seeds that heated soils do. The different antiseptics differ in the intensity of their action, but the inhibitory substance formed is probably 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 organic matter which was rendered soluble becomes insoluble, and the inhibitory action is reduced. This is also the case with heated soils, especially when repeatedly watered; though with unheated soils under similar conditions the soluble organic matter increases. The treatment of soils with antiseptics induces a change equivalent to that obtained by heating the soil to 60°—75°, and this may be sufficient to account for the increased growth observed in plants grown in them. The production by heat of a substance inhibitory to germination appears to be a property common to all soils, twelve instances having been examined: the proportion of it formed depends on the increase in the amount of organic matter rendered soluble by heating; but the actual amount of the soluble organic matter in the heated soil is not always a criterion as to the intensity of its inhibitory action, and still less is the amount of soluble organic matter originally present in the unheated soil, though in the majority of cases it may be so. There appears to be no connexion 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 favourably towards germination than pure water does: whether in any cases soils can act more favourably than water—as the earlier experiments had indicated they could—is open to doubt, but the probability is in favour of their doing so. So far as the instances now examined are concerned, the richer soils, and those containing most soluble organic matter, are slightly less favourable to germination than the poorer soils.