642 Waring ton.—The Effect of Boric Acid and Borax on 
again supplied with boric acid throughout the experiment. In order to 
prevent the transference of small traces of boron after the change, the 
roots were washed with distilled water, and as long as the size of the plants 
allowed of it clean bottles were used. 
The untreated set soon fell considerably behind all the others ; the 
short, thick type of root previously described for plants grown in the 
absence of boron was less evident, though the whole root system was poor. 
Seasonal conditions probably account for this, and the question is more 
fully discussed farther on. 
Another peculiarity of the plants receiving no boron was the outgrowth 
of numerous secondary branches. None of these tillers flowered, and in all 
respects they closely resembled the type of growth of the main axis. 
Brenchley (11 (a)) has described a similar bushiness of growth in peas supplied 
with toxic doses of boric acid ; but in the case of broad beans it would 
seem that the absence of an essential element was the factor concerned. 
(a) Death subsequent to the removal of boric acid. Each set as it was 
in turn deprived of boric acid gradually showed the characteristic £ dying 
off’, usually from three to six weeks after the transference into the normal 
culture solution had been made. 
Five weeks from the start of the experiment all the untreated plants, 
and several of those treated for ten days only, had begun to wither, while 
those which had been supplied with boric acid for thirty or more days were 
in flower and still growing rapidly. Although treatment for ten days 
was hardly beneficial, twenty or thirty days’ growth in boric acid caused 
a marked improvement, and a further superiority was seen in those supplied 
with H3BO3 for longer periods. 
After seventy days, all the plants which had been treated with 
1 : 50,000 H3BO3 were harvested. At this time, all such plants deprived 
of boron for forty days or longer were ‘ dying off’, but the remainder, with 
a single exception, were still healthy whether they had already been trans¬ 
ferred to the normal solution or were still supplied with boric acid. The 
1 : 2,500,000 sets, however, were carried on for twenty-six days longer, no 
further change in their solutions being made, all except five of the plants 
being already in the ordinary culture solution. 
At the end of this period every plant was either severely withered or at 
least showing signs of dying at the apex of the shoot, except the set of five 
which were still receiving boric acid ; the latter were perfectly healthy and 
even still flowering (PI. XIII, Fig. 7). 
It is clear, then, that a continual supply of boron enables the broad 
bean to make normal development, and that a comparatively large quantity 
given during the fiist few weeks of growth is less effective than a small 
amount supplied continuously. 
(b) dfjcet of tht concenti ahon of boric acid supplied. For the first week 
