137 
life and yield a crop comparable with that obtained with a good sup- 
ply of nitrate. The amount of nitrogen in the crop is sometimes a 
very large gain over that contained in the soil; this latter also occurs 
when the air is deprived of all ammonia, etc., and the nitrogen must be 
obtained from the free nitrogen of the atmosphere. But when the 
soil is sterilized by heat and the pots and seeds are sterilized as to 
their surfaces by washing with very dilute mercuric chloride, then peas 
behave like oats and barley; there is no gain of nitrogen from the air, 
the crops are proportional to the aie of nitrate in the soil, and 
no tubercles are formed on the roots. 
In all cases where the peas had gained nitrogen when planted in 
unsterilized soil, tubercles are formed on the roots, and, on the other 
hand, when they are planted in sterilized soil no tubercles are formed 
unless we add to the soil the washings of a small quantity of arable 
soil, in which case tubercles are generally formed. Such washings 
may themselves be sterilized by boiling or possibly by lower tempera- 
tures. 
The authors infer that the assimilation of nitrogen from the air 
by peas, lupines, and other leguminous plants is not within the power 
of the plant as such; nor can it take place when the plant grows 
within a sterilized medium, but is connected with the presence of mi- 
crobes and with the development of tubercles on the roots. (Agr. 
Ser Vole ELL, 9/2152) 
The fixation of nitrogen by Leguminose has been studied by E. 
Bréal, who succeeded in inoculating Spanish beans with bacteria from 
tubercles on the roots of Cystisa. At first the growth was vigorous, 
then the plant languished, but eventually recovered, flourished, and 
matured. Again, lucerne, growing in a pot in sandy soil, was inocu- 
lated by laying a fragment of tuberculous root of lucerne on the soil 
and watering the plant with drainage water. In both these cases not 
only did the plants gain in nitrogen, but the soils also, so that this 
experiment confirms the ordinary experience as to the behavior of 
the Leguminose as soil improvers. (Agr. Sci., Vol. IV, p. 79.) 
Lawes and Gilbert, in a memoir published in the Philosophical 
Transactions of the Royal Society of London for 1889, state their 
conclusions as to the sources of the nitrogen in the plant as follows: 
In our earlier papers we had concluded that, excepting the small 
amount of combined nitrogen coming down in rain and the minor 
aqueous deposits from the ‘atmosphere, the nitrogen source of crops 
was the stores within the soil and subsoil, whether from previous 
accumulations or from recent manuring. * * * With the Grami- 
new it was concluded that most, if not all, of their nitrogen was 
taken up as nitric acid. In leguminous crops, 1n some cases, the whole 
is taken up as nitric acid, but in other cases the source seemed to be 
inadequate. * * * Tt is admitted that existing evidence is insuf- 
ficient to explain the source of all the nitrogen of ‘the Leguminose. 
