Brenchley . — Organic Plant Poisons . /. 453 
tions of HCN growth was entirely suspended for about a month. At the 
end of this time most of the plants started into growth, slowly at first, more 
rapidly later on, so that at the end of the experiment they were healthy 
and fairly normal in type, but very small in size. With lower concentra- 
tions the initial delay in starting was less marked or did not occur at all, 
but the toxic action of the poison was very evident to the eye down to 
Gms. 
Fig. 1. Average dry weights of io series of barley plants grown in strong nutrient solutions 
in the presence of differing amounts of hydrocyanic acid. Feb. 16-April 18, 1914. 
Gms 
T ot,al 
Shoot 
Root 
ConcentratiorCwoo zo 10 5 33 1-5 2 « 0-4 oz. o-i o-ot o 
l =1:10,000,000 
Fig. 2. Average dry weights of io series of barley plants grown in weak nutrient solutions 
in the presence of differing amounts of hydrocyanic acid. Feb. 16-April 18, 1914. 
a very considerable dilution. From the outset the plants growing in the 
weaker food solutions were rather less developed than in the strong solu- 
tions, but the same order of development was maintained (Figs. 1 and 2). 
It was soon evident that the roots were able to withstand more poison in 
the strong solution than in the weak. With high concentrations, as 
1/100,000 and 1/500,000, the roots began to make growth at an earlier date 
in the strong nutrients, so that the plants pulled ahead and ultimately made 
