SCHREINER AND REED: EXCRETIONS BY ROOTS 283 
such an attempt they interpreted the failure of their analysis to 
mean that no excretions were produced by roots. They deserve 
credit, however, for showing that Brugmans had entirely misinter- 
preted the death of the root hairs and the peeling off of the outer 
layers of the root by assuming that this material was solid excre- 
tion from the living root. Nevertheless, several years later Gas- 
parrini (’57) made the absurd statement that he had observed that 
the root hairs had small lids which opened and emitted secretions. 
After the earlier work had been shown to be ill-founded by the 
investigations of Walser and Braconnot, that line of investigation 
Was given up, and it is only within recent years that any data have 
been presented on deleterious root excretions. 
Newcombe (’02), in describing the growth of roots in closed 
glass tubes containing water, says that the roots suffered distortion 
after 12 to 15 hours when the temperature was 23° C. or over. 
He referred the distortion to a possible lack of oxygen or to the 
accumulation of root excretions. 
Livingston (’05) described an experiment which indicated quite 
distinctly that toxic substances may arise during growth. The 
experiment consisted in placing an absorbent agent (carbon black) 
in a synthetic nutrient solution and measuring the growth of wheat 
plants in it. The plants from the nutrient solutions containing 
carbon-black grew 27 per cent. more than the control plants in a 
Solution in which carbon-black was lacking. In the solutions con- 
taining ferric hydrate the growth was increased 33 percent. In 
another experiment, water redistilled from potassium dichromate 
and sulphuric acid and from alkaline potassium permanganate was 
used, the distillates being condensed in a platinum tube. The 
addition of ferric hydrate to part of the cultures produced an 
increase of growth (measured by transpiration) amounting to 34 
Per cent. The conclusion was there drawn that the roots of 
Seedling wheat plants do give off substances which are poisonous 
to themselves, and that these substances can be removed or cor- 
rected by carbon-black of ferric hydrate. 
Indirectly there has been gathered some very good evidence 
"pon this point by investigators who have studied the antagonism 
between different species, 
The Woburn Experiment Station (’03) has reported a detailed 
