262 
Brenchley.—Organic Plant Poisons. II. 
start into activity of root growth was sharply reflected by the shoots, 
which improved greatly and lost some of their purple colour, though they 
remained small to the end. 
With the next strength, M/ioox 1/5 2 , a considerable initial check was 
evident, the roots being pinkish 
in colour. In about a fortnight 
the roots reached the bunchy 
stage, and after that rapidly im¬ 
proved, sending out long laterals 
into the solutions and eventually 
becoming almost normal in type- 
The effect of the initial check 
was visible in the brown dis¬ 
coloration which remained in the 
older part of the root, and also 
in the depressed dry weight. 
Growth steadily improved 
as the concentration decreased. 
There is just a hint of a pos¬ 
sible stimulation of growth with 
M/ioox 1/5 3 , as the plants are 
very considerably above the 
controls in weight. A similar 
result was obtained with another 
series later in the year; but there 
is not sufficient evidence to 
justify more than a suggestion 
that some stimulation may pos¬ 
sibly occur at this point ,provided 
the nutrient solutions remain 
unchanged throughout the course 
of the experiment. The rise 
does not occur if the solutions, 
and with them the supply of 
phenol, are renewed. 
In order to test the hypo¬ 
thesis that the decomposition 
or oxidation of the poison affects 
the plant recovery in the higher 
concentrations, three parallel 
sets of barley were grown : 
1 ^ H X 
/ 00 
5 
Fig. 3. Average dry weights of ten series 
of barley plants grown in strong nutrient 
solutions in the presence of differing amounts 
of phenol. Solutions never changed. April 
27-June 15, 1915. 
(1) Solutions never changed (Fig. 3). 
(2) Solutions changed once during the experiment (Fig. 4). 
(3) Solutions changed twice during the experiment (Fig. 5). 
