NOTE ON A TOXIC SUBSTANCE EXCRETED 
BY fit. ROOTS OF PEANTS. 
By F, FLETCHER, M.A., B.sc., 
Deputy Director of Agriculture, Bombay Presidency. 
Ir has more than once been suggested that plants, like 
animals, excrete (from their roots) material that is no longer of use 
to them or that are bye-products of the process of metabolism, 
and that such substances are injurious to the kinds of vegetation 
by which they are excreted. Brugmans was apparently the first 
to suggest this, and it has, at various times, been affirmed by 
Plenk, Humboldt, Cotta, De Candolle and others, denied by 
Hedwig, Braconnot, Walser, Boussingault, Unger, Meyen and 
others and has for long been considered as non-existent except 
with regard to carbon dioxide and possibly an acid phosphate and 
formates. 
Again, Dr. Gyde (Trans-Highland and Agricultural Society, 
1845-47, pp. 273-92) in water cultures obtained on evaporating 
the residual liquid, a very small amount of yellowish or brown 
substance, a portion of which was organic in character. He 
concluded that the amount excreted was very small, and that the 
substance was not injurious to the plants that gave rise to it. 
From observations on crops growing in the field, the writer: 
some years ago (while in Egypt) came to the conclusion that 
certain phenomena could only be explained on the theory of 
excretion. This was especially the case with cotton crops in 
which a grass was allowed to grow as a weed. The cotton, 
grown under irrigation, did not revive on application of more 
water ; its poor state was therefore not due to lack of moiscure 
in the soil. Manures likewise seemed to have comparatively little 
effect towards improvement ; appropriation by the weed of food 
materials was therefore not the cause of the poor growth. 
Aeration had as little effect as manure. 
LIBRARY 
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