272 Brenchley.—Organic Plant Poisons. II. 
the plants, except that in some cases the roots were rather discoloured. 
On the whole, to peas resorcinol is about as toxic as phenol itself, and much 
less toxic than most of the others of the phenol group. 
Barley is, as usual, more sensitive than peas (Fig. 13). With strong 
concentrations, including M/100 x the usual phenomena of intense poison¬ 
ing were noticed—belated start into growth, bunching of roots owing to 
reluctance of laterals to enter the solutions, poor shoot development, with 
purple coloration. No recovery was noted in these cases, so the dry 
weight remained low. With rather lower concentrations, again as usual, an 
initial check was followed by recovery—recovery so complete that the dry 
weights were fully equal to controls. No stimulation nor toxic action was 
observed in the greater dilutions of poison. 
Pyrocatechol. 
The general course of events was the same as with other phenols 
with which root recovery takes 
place at certain concentrations. 
Pyrocatechol is more toxic than 
many of the others, as with 
both peas and barley the harm¬ 
ful effects were noticed much 
farther down the scale. The 
behaviour of pea plants with 
M/ioox| poison was more 
noticeable (Fig. 14). The roots 
were killed beyond recovery at 
the very beginning and ra¬ 
pidly became grey, flabby, and 
mouldy. In spite of this the 
shoots continued to drag out 
an existence, and six weeks 
later actually came out into 
flower, though naturally the 
blooms were very small and 
poor. This is still more remark¬ 
able in that the concentration, 
M/ioox J, was not on the border-line of indifference, since with only one- 
fifth the strength, M/100 x 1/5 2 , very little root recovery occurred in any case, 
and even when it did take place it was only to a slight degree. 
The continuance of shoot growth after the death of the root was shown 
by the shoot-root ratio, which reached 10*5. As soon as root recovery set 
in the ratio rapidly fell towards that of the controls, which is about 4-3. 
gxvrr\s 
hu. 
i'Z 
ho 
•9 
•6 
*2 
y 
— 
/ f 
/ / 
/ t 
s f 
/ f 
/ 1 
/ / 
/ 
r 
t 
— 
— __ 
y 
TcitaX 
SKooV 
T^ooV 
5 - •* 
5 ^ 
r - 
loo 5 
Fig. 14. Average dry weights of ten series 
of pea plants grown in strong nutrients in the 
presence of differing amounts of pyrocate¬ 
chol. Sept. 29-Dec. 17, 1914. 
