Peas on the other hand are definitely stimulated with traces of boric acid, concentrations of 1/100,000 and less causing an improvement in growth, while under some experimental conditions even higher amounts of boric acid were beneficial. All the stimulated plants showed the characteristic dark green colour which seems to be associated with the presence of minute traces of boron in the nutritive solution. An interesting morphological feature was the strong development of small side shoots from the base of the plants in the presence of medium amounts of boric acid, from 1 part in 100,000 downwards. This gave rise to a certain bushiness of growth, which was less evident as the concentration of the stimulant decreased. The general outcome of the tests seems to be that boric acid needs to be supplied in relatively great strength to be fatal to pea plants, and that the toxic action gives place to a stimulative one high up in the scale of concentration. As far as experiments have already gone it seems as though the stimulation is not a progressive one, as the effect of 1/100,000 boric acid is as good as that of 1/20,000,000, a flat curve connecting the two. This, however, needs confirmation. Yellow lupins also give some evidence of stimulation with concentrations of about 1/50,000 boric acid, the improvement being far more strongly marked in some sets of experiments than in others. III. EFFECT OF BORON COMPOUNDS ON CERTAIN OF THE LOWER PLANTS. Our knowledge of the action of boron on the lower plants is less definite and complete than with regard to the higher plants. Morel (1892) found that boric acid acts as a strong poison to the lower fungi and similar organisms, their development being completely arrested by very weak solutions of the acid. He suggested, on this account, that boric acid might be used in the same way as copper to attack such diseases as mildew, anthracnose, &c., which attack useful plants. On the other hand Loew (1892) stated that such algae as _Spirogyra_ and _Vaucheria_ showed no harmful influence for many weeks when the culture water contained as much as ·2% (= 1/500) boric acid. This may be supplemented by a recent observation at Rothamsted, in which certain unicellular green algae (unidentified), were found growing at the bottom of a stoppered bottle containing a stock solution of 1/100 boric acid. Agulhon (1910 a) dealt chiefly with yeasts and certain ferments, and found that yeasts grown in culture solutions are not influenced favourably or unfavourably by relatively large quantities of boric acid up to 1 gram per litre, while all development is checked with 10 grams per litre. The presence of boron affects the action of yeast on glucose and galactose. Galactose alone is not attacked even after 40 days in the presence of ·66% boric acid. When glucose is mixed with the galactose the latter is said to be at first left untouched, but later it disappears very slowly.