294 Brenchley. — On the Action of Certain Compounds of 
in water cultures, and although the results must not be considered as 
conclusive, still they give certain indications as to the reaction of the genus 
to the poison, so a short account is here included. 
Barley . The initial experiments were carried out in July and August, 
1910, at a time of year peculiarly unfavourable to the growth of barley 
under the conditions appertaining to water cultures. Seedlings were treated 
with various amounts of boric acid grading from 1/5,000 to 1/20,000,000 in 
nutrient solution. In a very short time the effect of the boric acid was 
evident in the general dark green coloration of the plants supplied with it, 
except in those cases in which the concentration was so high as to cause 
decided poisoning. At a very early date the lower leaves of the latter 
plants presented a curious mottled appearance, turning yellow with big 
brown spots. Some trace of this discoloration was evident even with 
plants receiving only 1/500,000 'boric acid, but here only the tips of the 
leaves were affected. Towards the end of the experiment the shoots were 
badly attacked by rust and finally died off, so only the dry weights of the 
roots were determined in order to get some gauge of the effect of the poison. 
These dry weights indicated that i/joo,ooo B 2 0 3 exercised a very depressing 
action on the plants, but below this concentration no conclusions could be 
safely drawn. 
The above experiment was repeated twice in 1911, once in March and 
April, and again in May and June, but the concentrations were pushed still 
further, from 1/5,000 to 1/50,000,000 boric acid. In the first set all plants 
with more than 1/2,500,000 boric acid showed some trace of discoloration 
in the leaves within a week from the start, those with the higher concentra- 
tions already having the upper parts of the leaves spotted and very brown 
at the tips. This browning was seen first at the tips of the lower leaves, 
and then spread downwards as brown spots which coalesced, until finally 
the whole leaf was involved. The other leaves from below upwards were 
affected at a later stage with the higher strengths of boric acid, the mode 
of progression of the poisoning action being always the same. The plants 
were cut for drying after six weeks’ growth, at which time all those with 
weak solutions of boric acid were particularly dark green in colour, while 
all those with 1/2,500,000 boric acid and less showed a possible stimulus to 
the eye when compared with the control sets. On examining the dry 
weights of the plants it is evident that this stimulus was more apparent 
than real, the only plants which rose above the probable level of experi- 
mental error being those grown with 1/25,000,000 and 1/50,000,000 boric 
acid (Curve 15). 
In the later experiments a similar course of events was observed, 
except that a possible stimulation was obtained with concentrations below 
1/10,000,000 boric acid, the difference being probably the result of the later 
season. 
