270 
Brenchley.-—Organic Plant Poisons. II. 
means of greater root growth, and consequently the dry weights fall behind 
somewhat. The increase observed in the former case may be an instance 
of a local stimulation whereby increased growth is made to enable the 
organ concerned to cope with some special circumstance affecting the plant 
economy. This is quite different from stimulation in the ordinary sense, 
whereby the rate of growth of the whole plant is affected, giving corre¬ 
sponding increase in the dry weights of both root and shoot. 
In this connexion it is interesting to make a comparison of the shoot- 
root ratios in relation to the actual weights. With high concentrations of 
the poisons (except when root growth was so inhibited that death occurred 
early, so vitiating the value of any figures) the development of the roots in 
comparison with the shoots is much above normal, so that the shoot-root 
ratio is very low. This is what might be expected, as the action of the 
poison probably prevents a sufficient supply of food from entering the plant, 
so that if the latter is able to make any growth at all it concentrates its 
efforts first on extending the root system as far as possible in order to 
enlarge the absorbing area, improvement of the shoot following later, if at 
all, i. e. if the increase of root area is really associated with increased 
absorption. In the case under consideration with a particular concentration 
of poison, M/100 x 1/5 3 , the shoot reached a normal size, but to enable this 
amount of growth to be made the roots had to develop to an abnormal 
extent, so that the shoot-root ratio is still low. Below this concentration, 
when the action of the poison is very weak and the resistance of the plant 
is almost nil, the ratio approximates closely to the normal. 
Shoot-Root Ratio. 
Ortho-cresol. 
Meta-cresol. 
Para-cresol. 
Control 
2-744 
2-974 
2.638 
M/too x 1/5 
5.700 
1.960 
j.200 
M/100 x 1 /f. 2 
1 *955 
1.988 
1.681 
M/100 x 1/5 3 
2.252 
2.776 
2-367 
M/100 x 1/5 4 
3-156 
3* r 33 
3.013 
M/100 x 1/f 5 
3 *no 
2.907 
2.826 
M/100 x 1 /5 6 
2.983 
2-939 
2.748 
Resorcinol. 
The effect of very 
strong (M/100) resorcinol on 
peas (Fig. 
rather remarkable, on account of the great difference in the initial action of 
the poison on the roots and shoots. The roots were killed at once, as 
within two days they were white and flabby, and the parts above the solu¬ 
tions had begun to shrivel. In spite of this the shoots started into growth 
and made very fair development for several days, so that they were nearly 
as good as the controls, although by the end of the first week the roots were 
infested with a strong growth of mould. After ten days the shoots were 
much stronger than any others that had received the same concentration of 
