1906] BREAZEALE—EFFECT OF SOLIDS UPON GROWTH 63 
instance to get the same effect with sulfuric acid may be due to the 
fact that to be injurious this substance must be at a much higher con- 
centration than is needed in case of the copper salt, while the relative 
amount of solute absorbed by solids is much greater in dilute solutions 
than in more concentrated: ones. TRruE and OGLEVEE suggest this 
explanation for their failure to get marked improvement by the use 
of sand in solutions of phenol and resorcinol. 
On account of the presence of toxic substances in distilled water 
as ordinarily prepared, from copper boiler and tin condenser, most 
workers with toxicity problems have used water redistilled in glass. 
In these laboratories the distilled water is often quite toxic to wheat 
seedlings, but its injurious effect is prevented if it is first shaken with 
carbon black or ferric hydrate and the solid filtered off. It is found 
that water so treated produces as good a growth of seedlings as does 
the most carefully prepared redistilled water. 
It appears from these experiments (1) that extracts of certain soils 
are toxic to wheat seedlings in water culture, and that this toxicity is 
removed wholly or in part by carbon black, calcium carbonate, ferric 
hydrate, and other solids; (2) that the toxic substances of ordinary 
distilled water may be removed by ferric hydrate or carbon black; 
(3) that the roots of wheat seedlings give off substances which are 
toxic to themselves and that these substances can be made inactive 
by the presence of the last named solids in the culture medium; (4) 
that the presence of ferric hydrate and carbon black in the solution 
seemingly accelerates to a marked degree the development of roots, 
causing them to surpass the tops in growth. 
The work here reported was done chiefly in the laboratories of 
the U. S. Department of Agriculture, Bureau of Soils, Washington, 
D.C. It was finished at the Rhode Island Agricultural Experiment 
Station, Kingston, R. I. I am indebted to Dr. F. K. CAMERON, and 
to Dr. B. E. Lrvrncston, of the Bureau of Soils, for much valuable 
suggestion and advice. 
U. S. DEPARTMENT OF AGRICULTURE, 
Bureau of Soils, 
Washington, D. C. 
