egel, Wilfarth, Deherain, Joulie,
Dietzell, Frank, Emil von Wolff, Atwater, Woods, Nobbe, Ward, Breal,
Boussingault, Wagner, Schultz-Lupitz, Fleischer, Pagnoul, Schloesing,
Laurent, Petermann, Pradmowsky, Beyrenick, Lawes, and Gilbert.

It is impossible to enter into the details of these most important
experiments. An attempt may be made, instead, briefly to epitomise them.

_Recent Experiments on Nitrogen question._

In the first place, it may be asked, How is it possible that the
previous elaborate experiments, published prior to 1876, should now
prove unreliable? A satisfactory explanation may be found in the fact,
as Lawes and Gilbert have recently pointed out, that the fixation of the
free nitrogen by the plant, or within the soil, takes place, if at all,
through the agency of electricity or of micro-organisms, or of both.
The earlier experiments, however, were so arranged as to exclude the
influence of either of those agencies.

The question has further been limited in its scope. It is now supposed
that only plants of the _leguminous_ order have the power of drawing
upon the free atmospheric nitrogen. Of the experiments above referred
to, those of Hellriegel and Wilfarth are the most striking and
important. They found in their experiments, that while the legumes have
the power of obtaining their nitrogen from the air, cereals have not.
Similar experiments by Atwater in America, and others, support this
conclusion.

Their conclusions may be briefly epitomised as follows:--

(_a_) That the leguminous plants--such as peas, &c.--have the power of
drawing their nitrogen supplies from the free nitrogen of the air in a
way not possessed by other plants; and that they thus possess two
sources of nitrogen--the soil and the air.

(_b_) That this absorption of free nitrogen is not effected directly by
the plant, but is the result, so to speak, of the joint action of
certain micro-organisms present in certain soils and in the plant
itself, (_symbiosis_).

(_c_) That this fixation is connected with the formation of minute
tubercles on the roots of the plants of the leguminous class; and that
these tubercles may be the home of the fixing organism.

(_d_) That these fixing micro-organisms are not present in all
soils.[27]

While the relation of free nitrogen to the plant has long been, and
still is, a very obscure problem, it was early recognised that the
combined nitrogen present in soils and manures was an import