PROCEEDINGS OF SECTION K. 647 



Cjuinone is an oxidizing agent, and its ill-eSects are less marked 

 when the plant is supplied with relatively large proportions of 

 sulphate of potash which has a known influence in restraining root- 

 oxidation. 



A fourth substance is coumarin, a substance of fairly wide dis- 

 tribution in the vegetable kingdom, and found to be toxic to many 

 plants. Schreiner and Skinner (loc. cit.) find that it is particu- 

 larly toxic to wheat, the leaves being short and broad, and the 

 roots discoloured, and their surface very shiny. The harmful effect 

 of this substance was greatest when phosphoric acid was absent 

 from the nutrient solution, and practically disappeared when the 

 fertilizer was rich in phosphates. The same results were obtained 

 with wheat-plants grown in soil in culture-pots. 



It would therefore appear that the bad effects due to the pre- 

 sence of dihydroxystearic acid and of vanillin can be, to a large 

 extent, neutralized by the application of sodium nitrate, those due 

 to coumarin by phosphoric acid, and those due to quinone by sul- 

 phate of potash. With the exception of coumarin these experi- 

 ments were carried out apparently only in water-culture experi- 

 ments, and the point must not be lost sight of that these results 

 when tried in the field may be considerably modified by the 

 chemical or physical nature of the soil. They are sufficiently 

 striking to emphasize the fact that the function of fertilizers is not 

 solely to supply plant food. 



Fungi Affecting Crops. 

 Another way in which one crop may affect injuriously a suc- 

 ceeding crop is by the production of a fungus which infects the 

 soil and attacks the young plants. A fungus of this nature has 

 been found by H. L. BoUey (Bulletin No. 50, North Dakota Agri- 

 cultural College, 1901), to be the cause of what are known as flax- 

 sick soils, that is, soils which, after continuous cropping with flax 

 (which does not unduly exhaust the soil) are unable to produce 

 flax. He quotes an experiment in which flax was grown for six 

 consecutive years on a fertile soil of the Red River, the result 

 being that tlae land was " in such a diseased condition that not a 

 plant of flax can exist on it longer than three weeks from the time 

 of sowing." This condition of things is well known in Europe and 

 America to flax-growers, and it is the custom, in Europe at all 

 events, to sow flax at intervals of not less than eight years on the 

 same land, the flax being part of a rotation including turnips, oats, 

 clover, wheat, and beans. 



Bolley has found that this flax-sickness is due to the growth of a 

 fungus which he calls Fusarium lini, which lives in the humus of 

 the soil, and attacks the flax-plant. 



