264 Brenchley.—Organic Plant Poisons. II. 
With the controls and with the lower strengths in which the phenol 
had apparently reached its indifferent point the growth of the barley was 
much better when the solutions were renewed than when they were never 
changed. This is in accordance with other work and is independent of the 
concentration of the nutrient solution. 1 With the higher strengths of phenol, 
which are toxic, increase of growth did not run parallel with renewal of food 
solution ; but, on the contrary, the actual growth as shown by the dry weight 
was in inverse ratio to the frequency of renewal. 
Table I. 
Dry Weights of Barley Plants. Mean of ten Plants. 
Sols, never changed. Sols, changed once. Sols, changed twice, 
grm. gnu. grm. 
M/100 x 1/5 0-525 0.T50 0.117 
M/iooxi/5 2 1-910 1-651 0-871 
The figures in Table I show very clearly that root recovery and the 
ultimate improvement of growth are associated with the decomposition of the 
poison. With M/ioox-g- the decomposition had not proceeded far enough 
in any case to allow the inhibitory toxic factor to be more than counter¬ 
balanced by the inherent vitality of the root. Consequently root recovery 
could not begin to set in before a fresh supply of phenol was presented to 
the plant, even when the solution was only changed once. When no renewal 
was made the roots were able to make some amount of recovery, but the 
strength of the poison was so great that this was comparatively slight. 
With M/100 x 1/5 2 , on the other hand, the decomposition of the poison 
was counterbalanced at an earlier date by the plant’s vitality, so that root 
recovery set in before the renewal, when the solutions were only changed 
once. When growth had made a fair start the plants were more resistant to 
the action of the fresh supply of phenol, so that the ultimate growth was not 
so very far behind that of the plants with which no renewal had been made. 
When the solutions were changed more frequently, root recovery was still in 
abeyance or had only just begun when a fresh supply of poison was presented, 
consequently recovery was thrown back considerably, and though the roots 
proceeded slowly to form new laterals a further check took place with the 
second renewal, and the ultimate growth was much less than that of all the 
other plants, in which the solutions were changed once or not at all. By 
the time of cutting the plants had apparently got a grip on life, and judging 
by their appearance it is possible that if they could have been grown on 
longer they might have made up their deficiency at a more rapid rate. It 
seems that when once growth is fairly under way and vigorous, the plants 
can cope with a strength of poison which is most deleterious at an earlier 
stage of development. 
1 Brenchley, W. E. : Ann. of Bot., vol. xxx, pp. 77-90. 
