646 Waving ton .— I he Effect of Boric A. cut and bovax on 
earlier work and also with the experiments on the broad bean here 
described. I11 general, the results are in close agreement with those of 
Brenchley, in spite of the fact that in the 1914 work the nutrient solutions 
were never renewed and the plants were harvested at a comparatively early 
stage, so that the action of boron is apparently similar whether in the 
presence of a plentiful or restricted food supply. The barley seed used in 
3921 was an unnamed pure strain from Professor Biffin, but in the following 
season the variety was pure line Goldthorpe from Leamington. In each 
case the seed was graded by weight to within o-oi grm. 
a. The Effect of Different Concentrations of Boric Acid in the Nutrient 
Solution. 
In the preliminary experiment the effect of a wide range of concentra¬ 
tions was tried, viz. from 1 :5,000 to 1 : 100,000,000. Five plants were taken 
as the unit in this case. 
(a) Development of the root. The plants treated with 1 :5,000 H 3 B 0 3 
showed the injurious effect of boron after as little as three days’ growth in 
the solution. The roots were thick and short, and curled root-tips were 
noticed in several cases. Later a number of long, fine laterals were pro¬ 
duced, resulting in a bushy appearance. A gradual improvement in the root 
development was evident as the concentration of boric acid was reduced, no 
bushiness being noticeable when less than 1 : 50,000 H 3 B 0 3 was given, while 
the 1 : 2,500,000 and weaker sets closely resembled the untreated plants. 
if) Development of the shoot. The 1:5,000 set soon showed the toxic 
effect of boron. The leaves turned yellow at the tip, and later brown spots 
appeared, beginning at the apex and margins and gradually covering the 
entire leaf-blade. As fresh growth was produced it was rapidly affected in 
the same way, the injury always appearing first in the lower leaves. The 
nature and mode of progression of the poisoning action were exactly similar 
to that previously described by Brenchley (11 ( a )). The leaves were small 
and narrow, and in every case the plants were poor and scarcely tillered and 
never came into ear. The flecking of the leaves gradually disappeared as the 
quantity of boric acid supplied was decreased, and in the plants grown with 
1 :500,000 and 1: 2,500,000 the discoloration was very slight ; both these 
sets also came into ear. The plants grown in 1 : 2,500,000 and 1 : 12,500,000 
h 3 bo 3 were the best in this series. They were taller and a darker colour 
than the controls and appeared particularly healthy. This dark-green 
coloration is apparently typical of plants treated with non-toxic doses of 
boric acid, and has also been previously noticed. 
No stimulating effect, however, was apparent in the plants grown with 
1 : 100,000,000 H 3 B 0 3 ; they in all ways closely resembled the controls, the 
latter being healthy and well grown. 
