The Woburn Pot-Culture Experiments , 1907-8. 359 
the trial of the new inoculating material, “ nitro-bacterine,” 
for leguminous crops ; as also in the further examination of 
the question of “ soil-acidity.” 
The Hills’ Experiments continue to show in a remarkable 
manner how very potent is the influence, both on germination 
and on crop return, of even very minute quantities of salts of 
certain of the rarer bodies, such as lithium and manganese. 
With lithium, the sulphate, chloride, nitrate, and carbonate 
were all tried, but whereas in 1906 the quantity of the metal 
(lithium) applied in these several forms was as little as ‘05 in 
100 parts of the soil, in 1907 the amount had been reduced 
to ’0075, and in 1908 it was still further reduced, viz., to 
•00375 parts in 100 parts of the soil. It was found in 1908 
that even this small quantity retarded germination materially 
and also reduced the crop. In the case of carbonate of lithium 
the decrease of crop was about 50 per cent., and with the 
nitrate 25 per cent. 
It has all along been known that even small quantities of 
certain salts introduced into solutions in which plants are 
growing (water-culture) are capable of exercising marked 
effect upon the growth, but it was not until these Pot-culture 
Experiments were carried out that one believed that the 
presence in quite small quantity, in the soil, of ingredients of 
unusual nature and occurrence could exercise so remarkable 
an influence on vegetation as was shown to be the case. 
Incidentally this throws light upon the next subject that was 
specially studied in 1907-8 — the injurious nature of the acidity 
produced on the soil of the continuous wheat and barley 
experiments (Stackyard Field), where ammonia salts had been 
used year after year. 
That the material producing this acidity exists in but small 
quantity has been shown, but equally is it exceedingly potent. 
In 1907-8 it was sought to ascertain whether this acidity could 
be destroyed by the use of any oxidising agent. With this 
view, sulphate of iron, sulphate of copper, pyrogallic acid, and 
animal charcoal were severally tried. While the results with 
the three first named were neutral, there was a singular result 
obtainable from the use of animal charcoal, the previously acid 
soil (which would not grow barley) being now rendered 
capable of bearing a barley crop, although the quantity of 
animal charcoal applied was not more than 1 1 (5 per cent, of 
the weight of the soil. Whether the animal charcoal works by 
reason of the absorption of the injurious substance in the soil, 
or by virtue of the lime contained in it, is a point that is now 
being further investigated. 
Equally interesting is the next set of experiments — the 
continuation of the work on the relation of magnesia to lime 
