634 Waring ton .— The Effect of Bone Acid and Borax 011 
type of root was most distinctive, being short and thick with a stunted 
appearance 1 (PI. XIII, Fig. 1). However, the individual variation was very 
great and a few isolated cases occurred with the long thin type of root, which 
was that universally met with among the plants supplied with boric acid 
(PI. XIII, Fig. 2), but in no case was a good root system developed. 
While the contrasts between the root development of the individual 
sets supplied with different concentrations of boric acid were much more 
strongly marked in the early stages of growth, the difference between the 
controls and all the boron-treated plants became more evident as growth 
went on, suggesting that it was the presence or absence of boron that was 
the important factor, rather than the actual concentration of H 3 B 0 3 supplied. 
That this was the case will be more clearly seen after development of the 
shoot has been considered. 
(, b ) Development of the shoot. Differences between the various sets 
became noticeable in the development of the shoot slightly later than in the 
case of the roots ; however, a clear contrast was evident after about ten days’ 
growth in their respective solutions. 
H 3 B 0 3 i : j,000. 
These plants offered a marked contrast to all the others, both in colour 
and appearance of the shoot. From the first they were rather less forward 
than those receiving smaller doses of boric acid, but were well ahead of the 
controls. Besides presenting a flaccid appearance, many were pale yellow, 
and although they became a better green colour later, the leaves frequently 
turned brown and withered along the margins. The lower leaves were the 
first to become affected, but towards the end of the experiment quite 
a number of the upper leaflets showed it too. A similar condition of the 
leaf has been described by Brenchley (11 (a)) for peas grown in high concen¬ 
trations of boric acid. In the experiment carried out in the spring the 
plants were much more severely injured than those receiving exactly the 
same treatment during the summer months. This was probably due to the 
fact that both the rate of growth and the vitality of the plant would be less 
vigorous in the early part of the year than during the summer, and con¬ 
sequently the plant would be less able to resist the influence of the poison. 
A similar relationship between the season and the degree of toxicity of 
a given amount of poison has been more fully described by Brenchley 
(11 (a)) in the case of the action of both zinc sulphate and boric acid on peas 
and barley. 
H 3 B 0 3 1: 2j,ooo, 1: jo,000, and 1:100,000. 
These three sets soon ran ahead of all the others, and for some time 
were decidedly the tallest plants, though this distinction in height gradually 
disappeared towards the close of the experiment. 
1 See note at end. 
