Brenchley.—Organic Plant Poisons . II. 277 
a very short time after the plant comes in contact with the solutions. 
Occasionally, as with resorcinol and orcinol on peas, the shoots continue to 
make a certain amount of growth for a few days, even though the roots are 
killed. Apparently the toxic principle in these cases is not conveyed to the 
leaves at once, so that they are able to grow for a time at the expense of 
the food stored up in the seeds. More usually, however, the growth of the 
shoots is checked simultaneously with that of the roots, though the leaves 
retain their green colour for quite a long time before they wilt. 
The difference in the relative toxicity of the phenols is well shown by 
the action of solutions one-fifth as strong as the above (M/ico x i). Marked 
toxic action is evident at the first in every case, and the roots are often 
killed and discoloured. 0-Cresol, pyrocatechol, and pyrogallol kill peas 
outright at this strength, but with the other substances the roots make an 
attempt to right themselves after some time has elapsed. New laterals are 
pushed out, which frequently refuse to enter the solutions, so that the 
recovery is only partial. 7/^-Cresol admits of only very slight recovery with 
peas ; ^-cresol, phenol, and phloroglucin permit rather more ; while with 
resorcinol and orcinol quite good root development is able to take place 
ultimately, with which a corresponding improvement in the shoot growth is 
associated. Barley is more sensitive than peas, as recovery seldom takes 
place, and even with resorcinol and orcinol the roots make very little 
improvement. 
The lower strength, M/100 x 1/5 2 , also shows clearly the difference in the 
action of the phenols, the range of variation being considerable. In nearly 
every case an initial check is evident, but the degree of injury varies very 
much. Resorcinol at this strength has very little effect on peas, as growth 
is fairly good from the beginning; and with orcinol, too, strong growth is 
made. Phenol makes the roots bunchy when they put out laterals, but the 
recovery is so complete that the plants make nearly as much dry weight as 
the controls. Recovery is variable in amount with most of the other 
substances, but pyrocatechol is so poisonous that very little growth is 
made up to the end. Barley behaves in much the same way as peas, though 
owing to its sensitiveness the recovery is not always so complete as in peas. 
Lower concentrations of all the poisons do not seem to exercise injurious 
action on growth. 
2. The root recovery observed in strong solutions suggests that in these 
cases the poison acts largely by suspending the activities of the plants, 
paralysing it without killing it outright. Consequently, when the paralysing 
effect wears off or when the concentration of the solution is somewhat 
reduced by oxidation (in cases where this occurs), then the plant reasserts its 
vitality, struggles to put out lateral roots, and frequently succeeds so well 
that fairly good growth is eventually made. 
3. No signs of stimulation have been observed with any of the phenols 
