Organic Plant Poisons. 
II. Phenols. 
BY 
WINIFRED E. BRENCHLEY, D.Sc. 
Rothamsted Experimental Station. 
With eighteen Figures in the Text. 
T HE phenols form a group of organic compounds that suggest possi¬ 
bilities with regard to the partial sterilization of soils. On this account 
experiments have been carried out to gain some idea of the action of these 
substances on the plant itself, apart from the partial sterilization effects 
which occur in treated soils. In soil culture the action is largely, if not 
chiefly, indirect, by way of the increase of the available food supply ; this 
indirect action is usually so strongly marked that any direct action, whether 
beneficial or adverse, is masked. In water cultures the partial sterilization 
effect is absent on account of the lack of available organisms in the shape of 
protozoa and bacteria, so that the direct action of the phenol on the plant 
may be observed. 
The whole series of experiments were carried out systematically on 
parallel lines, to admit of comparisons between the action of one phenol and 
another. The solutions in each case were made up on the basis of the molecular 
weights of the poisons, the strongest solution in each case containing M/ioo 
grammes per litre, each of the succeeding strengths being one-fifth of that pre¬ 
ceding—i.e. M/ioox-l, M/iooxi/5 2 ,. ..M/iooxi/6 6 — allbeing matched 
against controls receiving no poison. In most cases the usual Rothamsted 
solution was used, but occasionally comparisons were made with results from 
a weak nutrient solution. 
Strong nutrients (.Rothamsted solution). 
Weak nutrients . 
gnn. 
grm. 
Potassium nitrate . 
. . 1*0 
0*2 
Sodium nitrate .... 
— 
°*5 
Magnesium sulphate 
o *5 
OT 
Calcium sulphate .... 
c -5 
o-r 
Potassium di-hydrogen phosphate . 
o -5 
0*1 
Sodium chloride .... 
0.5 
O’1 
Ferric chloride .... 
0-04 
0-04 
Distilled water, to make up . 
1 litre 
1 litre 
Phenol. 
Parallel sets of peas were grown with strong and weak nutrients 
(Sept. 24 to Dec. 5). M/100 proved to be a virulent poison. Within 
two days of insertion the parts of the roots above the solutions were all 
utterly shrivelled, whereas within the solution they were very white, 
rather swollen, and flabby, with a most unnatural appearance. The 
[Annals of Botany, Vol. XXXII, No. CXXVI. April, 1918.] 
