1906] BREAZEALE—EFFECT OF SOLIDS UPON GROWTH 61 
densation being carried on in a platinum tube. Upon this water the 
effects of carbon black and ferric hydrate were tested, the solids 
remaining in the water during the growth of the plants. The former 
gives little or no increase in transpiration, the latter a moderate 
increase, but both solids produce’a marked acceleration in root growth. 
Twelve seedlings grown fifteen days in redistilled water with and 
without ferric hydrate are shown in fig..4. No. 1 shows those from 
the untreated water, no. 2 those with the solid. The water here used 
probably did not contain injurious substances, and therefore the effect 
of the solids is most probably due to the removal of some injurious 
exudation arising from the plants. Further, distilled water in which 
plants have been grown for a number of days is found to give less 
growth upon replanting than does unused water, and the injurious 
effect of the used water is corrected by shaking with carbon black or 
ferric hydrate and filtering off the solid. Thus it seems that wheat 
seedlings do give off bodies from their roots which are toxic to them- 
selves. 
When the work so far recorded was practically completed, the 
appearance of TRUE and OGLEVEE’s paper® on somewhat similar 
experiments made it seem advisable to withhold publication until 
some further tests suggested by that paper could be made. These 
authors find that by the introduction of sand, filter paper, parafiin, 
or potato starch into solutions cf copper sulfate in which seedlings 
of Lupinus albus are growing, the toxicity of the solute is remarkably 
decreased. By this means the killing concentration of the salt may 
_ be effectively reduced, according to the amount of the insoluble body 
present, either to a stimulating concentration or to one in which the 
physiological effect is not apparent. They. reasoned that the solid 
absorbed the salt from the solution and in this way produced an effect 
closely paralleling that of simple dilution. 
It was determined to test the effect of solids in solutions of sulfuric 
acid. Maize was here used instead of wheat. First, the strength 
of this acid necessary to prevent the growth of maize seedlings was 
6 True, R. H. and Octever, C. C., The effect of the presence of insoluble sub- 
stances on the toxic action of poisons. Science N. S. 19:421-424... 1904. 
Bot. GAZETTE 39:1-21. 1905. In this connection see also DANDENO, J. B., The 
relation of mass action and physical affinity to toxicity, etc. Am. Jour. Sci. 17: 437- 
458. 1904. 
