March, 1912.] 



231 



Scientific Agriculture, 



different seasons in the year ; but the re- 

 sults in every case showed, contrary to 

 expectation, that the soil from the grass- 

 ed ground was slightly more favourable 

 towards germination than the tilled soil. 

 These results, of coures, afford no 

 direct evidence in favour of the presence 

 of a toxic substance in grassed soils, 

 though they are quite consistent with 

 such a view, for a toxic substance, if 

 present might, just as in the case of 

 heated foil, give rise, on decomposition, 

 to conditions specially favourable to- 

 wards germination. It was noticed, 

 also, that in most cases the soil which 

 had been under grass absorbed water 

 much less readily than the neighbouring 

 tilled soil, a behaviour which is highly 

 suggestive, inasmuch as the same 

 character is observed in heated soils in 

 contrast with unheated ones. 



Strong evidence of a positive character 

 as to the formation of a toxic sub- 

 stance during the growth of grass was 

 finally obtained from various series of 

 experiments with trees grown in pots. 

 It was found that such trees, when 

 watered with the leachings obtained 

 from trays containing grass growing in 

 sand, flourished more than when water 

 alone was supplied ; but when the tiays 

 were placed on the surface of the soil 

 (or sand) in which the trees were grow- 

 ing, so that the washings from the grass 

 reached the tree-roots with practically 

 no exposure to the air, they then had a 

 very deleterious effect, nearly if not 

 quite as great as when the grass was 

 grown above the roots of the trees in 

 the ordinary way. The trays contain- 

 ing the grass were movable, and the 

 sand in them, with the grass growing 

 in it, was separated from the medium 

 in which the trees were growing by the 

 perforated iron bottoms of the trays 

 and a sheet of wire gauze ; moreover, 

 the contact between the bottoms of the 

 trays and the sand or soil beneath 

 would be, at the best, very imperfect, 

 so that it is impossible to explain the 

 action of grass in such a case by the 

 abstraction by the grass of anything 

 from the soil (or sand) below the trays, 

 and it must be due to the passage of 

 something from the trays down to the 

 trees. The experiments on this subject 

 were numerous, and the grass-effect was 

 uniformly shown in all of them ; and, it 

 should be mentioned, the trees without 

 grass, with which the grassed trees were 

 compared, were grown with trays of 

 sand above their roots, so as to exclude 

 the possibility of explaining the results 

 by the mere presence ot the trays. 



The ready oxidisability of the toxic 

 matter formed by grass into some sub- 



stance which favours plant-growth will 

 explain the previously observed bene- 

 ficial effect of grass-leachings in cases 

 where these had been exposed to air, 

 and also why soil taken from grass 

 ground should be more favourable to 

 plant growth than that from tilled 

 ground. All this in the full accordance 

 with what has been established as to 

 the behaviour of heated soils towards 

 plants, where toxic matter is formed by 

 the heating, and increased fertility 

 follows its destruction, and is in accord- 

 ance also with the results obtained 

 with the germination of seeds in soil 

 from grassed and ungrassed ground, 

 the time elapsing between the drawing 

 of the samples and the germination of 

 the seeds being sufficient for the con- 

 version of any toxic substance present 

 into a beneficial substance. 



THE SOIL AND THE PLANT : A 

 REVIEW OE SOME RECENT 

 AMERICAN HYPOTHESES. 



By Edward J. Russell, D.Sc, 

 (London), 

 Goldsmith Company's Soil Chemist, 

 Rothamsted Experimental Station. 



(From Science Progress, Vol. VI., 

 No. 21, July, 1911.) 



In order that the reader may be in a 

 position to appreciate the exact force of 

 the hypotheses to be discussed here, and 

 to understand the precise bearing of the 

 points at issue in the controversies to 

 which they have given rise, it is desir- 

 able at the outset to state briefly the 

 salient features of the relationship be- 

 tween soil and plant. 



Various conditions have to be fulfilled 

 in order that a plant may make satis- 

 factory growth : there must be sufficient 

 food, water, air, warmth and light, also 

 there must be an absence of harmful and 

 inhibiting factors. Further, if the plant 

 is to be grown economically and without 

 undue risk of loss, the soil must provide 

 a sufficiently firm anchorage ground, so 

 that the plant can stand up well and not 

 suffer too much from wind. For our 

 present purpose we may dismiss the 

 action of light as being unconnected 

 with the soil and group the remaining 

 requirements in two main classes : food 

 supply and certain inhibiting factors, 

 which are largely connected with the 

 chemical properties of the soil, form the 

 one ; the water, air, temperature and 

 root-hold factors, which are more closely 

 related to its physical properties, the 

 second. The distinction is further con- 



