Brenchley.—Organic Plant Poisons . IP 269 
ultimate results were variable, some plants being strong and healthy, others 
small and weakly, but the general growth was much better than in either of 
the other cresols. With both m- and /-cresol root growth was greatly 
checked at first; the roots became bunchy, not entering the solution for some 
time, but later on thick laterals were formed, which pushed down into the 
water. The shoots were small and fairly healthy, but they showed purple 
coloration in the stem. The recovery was less in both cases than with 
0-cresol. 
M/100 x 1/5 3 . With 0- and M-cresol growth was normal from the first, 
though for a time some slight 
check to the rate of growth 
was evident. This was over¬ 
come later on, and the plants 
pulled up to the level of the 
others receiving less poison. 
With /-cresol the roots were 
very short and bunchy at the 
beginning, and did not begin 
to struggle ahead for about 
a fortnight. When once the 
long laterals began to form and 
enter the solutions the improve¬ 
ment in growth was very rapid 
and the plants made up most 
of their leeway. 
It is noticeable that in all 
three cases the barley receiving 
the next strength of poison, 
M/too x 1/5 4 , made less growth 
than with the higher concen¬ 
tration just described. This 
drop was chiefly in the root, 
being much less marked in the 
shoot. As the concentration de¬ 
creased from this point, the dry 
weights increased steadily towards that of the control. As this happened 
consistently with all three cresols it is quite probable that it is a true 
phenomenon. With the M/ioox 1/5 3 strength the balance of warfare be¬ 
tween the plant and the poison is very nicely balanced, and it is possible 
that in its strong efforts to gain the upper hand the plant developed a very 
extended root system and made a fuller use of the food supply, resulting 
in a greater dry weight. Apparently the whole effect of the poison is 
not lost with rather lower concentrations, but the toxic action is so 
slight, that the plant does not make the same effort to overcome it by 
Fig. it. Average dry weights of ten 
series of barley plants grown in strong nutrient 
solutions in the presence of differing amounts 
of/-cresol. March 13-April 26, 1915. 
