640 CONTRIBUTIONS TO OUR KNOWLEDGE OF SOIL-FEKTILITY, xiii., 



soil-extracts, and my experiments liave shown tliat the toxicity 

 is only apparent when the ratio of water is about 1:1. It would 

 be necessary to use this ratio in order to obtain leachings, for a 

 smaller quantity of water, say a ratio of 1 : O'O, would simply 

 wet the soil. My experiments with bacteriotoxins have shown 

 that tliehalf ratio gives an extract which is nutritive to bacteria, 

 just as it is to plants. The toxicity of the leachings and the 

 beneficial effect of the simple wetting appear to bring the bac- 

 teriotoxins into line with the plant-toxins, and make it possible 

 that they are similar, if not identical. 



If the root-debris consists of the shrivelled root-hairs, it is a 

 substance which will decay with comparative slowness, and we 

 should expect very little toxin to be developed in a month, a 

 usual time for laboratory experiments. This is really what 

 occurs; a comparatively small amount of toxin does develop. 

 But I have found that, in the open soil under grass, the produc- 

 tion of toxin is much quicker, and this leads to the supposition 

 that some quickly decomposing substance is given to the soil by 

 the grass. Some years ago. Maze* showed that a gramineous 

 plant, maize, secreted dextrose. In water-culture experiments 

 under aseptic conditions, he found this sugar in the water bathing 

 the roots of his plants. If this is the case, for it has not been 

 confirmed, we have a reason for the rapid production of toxin in 

 the soil in which plants such as grass are growing. 



It has been known for some time that crops are injuriously 

 affected by the presence of easily fermentable carbohydrates in 

 the soil. The deleterious action of raw farmyard-manure upon 

 certain soils is an example. Russell showed that, unless time 

 were given for starch to decay, its addition to soil was followed 

 by a diminution of the crop. Lipmanf showed that the addition 

 of glucose to soil depressed the yield of crop even when an excess 

 of fertilising material, including nitrate, was present, and, 

 furthermore, that the depression of the crop was not due to the 

 action of denitrification of the nitrate by bacteria or moulds, as 

 nitrates were found in the affected crop. 



* Aiiual. de I'lnst. Pasteur, xxv. (1911), p. 724. 

 t Lipmaii, New Jersey Agric. Expt. 8tn. Rept. No.257. 



