IOO 



PHYSIOLOGY OF NUTRITION 



in connection with which they were produced, and this may explain the fact that 

 a soil that is unproductive for tomatoes may still produce a good crop of 

 grain. Cultures in water extracts of unproductive soil give but poor growth, 

 but growth is improved proportionally with the dilution of the extract with 

 distilled water (Fig. 64). Addition of lime frequently neutralizes the toxic 

 effect. To secure a good crop in an unproductive soil that contains toxins, it is 

 necessary to find substances or treatments that render the soil toxins harmless. 

 The effects of water extact from bog-soil and those of bog water, upon the 

 development of Vicia faba 1 (Windsor or broad bean), are shown in Fig. 65. 

 The addition of calcium carbonate and the adsorptive action of carbon- 



FiG. 64. — Wheat plants grown in extract of toxic soil. 1 and 2. undiluted extract; 3 and 

 4, equal parts of extract and distilled water; 5 and 6, one part extract diluted with nine parts 

 of distilled water. (After Schreiner and Shorey. Reproduced by permission of U. S. Dept. 

 Agric, 1909.) 



black have been very effective here. In this case the toxic action of the bog 

 water was probably due to toxins arising from the microorganisms of the soil, 2 

 rather than to toxins emanating from the bog plants.^ 



1 Dachnowski, Alfred, The toxic properties of bog water and bog soil. Bot. gaz. 46: 130-143. 1908. 



2 Lohnis, F., Hanbuch der landwirtschaftlichen Bakteriologie. Berlin, 1910. 



k That bog waters are toxic to ordinary plants (at least, in that they have an acid reaction), 

 has long been suspected. Schimper (Schimper, A. F. W., Plant geography upon a physiologi- 

 cal basis. Translated by W. R. Fisher. Oxford, 1903) considers bogs as physiologically dry, 

 but is not clear as to just what physiological dryness may be due to. Livingston tested the 

 two logical possibilities in this case. He found (Livingston, B. E., Physical properties of bog 

 water. Bot. gaz. 37: 383-385. 1904) that high osmotic concentration of bog water is 

 not a possible explanation of physiological dryness; bog water has a freezing-point no lower 

 than that of water from drained swamps and rivers of the vicinity. By the use of an alga 

 as a physiological indicator, the same author showed very clearly that bog waters usually 

 contain toxic substances. (Livingston, B. E., Physiological properties of bog water. Bot. 



