March 1, 1900.] Supplement to the " Tropkal Agrimltunst." 
641 
Mr. Joliii HuuLer, r.LC, F.e.5., Chemical Analyst 
and Lecturer on Agricultural Chemistry and Brew- 
ing Science. The other was Professor McAlpine, 
Lecturer on Botany .ind Botanical Adviser to the 
Highland and Agricultural Society of Scotland. 
The discoTeries of Pasteur and other investiga- 
tors as to the paramount importance of having 
the right crops of yeast plants in the produc- 
tion of bear were doubtless the means by which 
Mr. Hunter was led to recognise the equally 
great importance of having in the soil the right 
crops of soil bacteria. The nodules on the roots 
of the leguminosae were first investigated by 
Messrs. Hunter and McAlpine, and, as the results 
of a careful series of investigations and experi- 
ments, they demonstrated the fact that the bac- 
teria in these root nodules did possess the power 
of absorbing the " free nitrogen " of the atmo- 
sph«re and rendering it available for the use of 
the plant. The discovery of this property on 
tbe part of the nodule bacteria is usually as- 
cribed to Hellriegel, but years before Hellriegel 
announced his discovery in 1886, Messrs. Hunter 
and McAlpine were teaching the same fact to 
tkeir students, aa the lecture notes of any of 
their students at that time can testify. After 
investigating the nature and functions of the 
bacteria in the root nodules of the leguminosae, 
Meisrs. Hunter and McAlpine proceeded to 
garry out a series of investigations in regard to 
the nitrifying bacteria. At an early stage of 
their investigations they found there were several 
well-defined sets of bacteria concerned in the 
■work whose final end is nitrification. They suc- 
ceeded in isolating and cultivating the nitrous 
germs, and they also isolated what they believed 
to be the nitric germ, but in the case of the 
latter germ they were tor a time puzzled to 
find that they could not from it, in any ordi- 
nary culture media, produce nitrates. By a happy 
inspiration they remembered the plan by which 
Napoleon was able to secure from the old mortar 
in the Paris stables a supply of nitrate for the 
manufacture of gunpowder, and they accordingly 
added a small supply of mild lime in the form 
of garden wall mortar to the culture media, 
with the result that the nitric germs produced 
nitrates speedily enough. These experimentors 
knew well enough before then that caustic lime 
would destroy the soil bacteria, and they therefore 
taught that the old plan of applying a heavy 
dressing of four to six tons per acre of hot 
lime was a huge mistake, while on the other 
hand a small annual, or at the outside bien- 
nial dressing of lime compost to the surface soil, 
where bacterial life was most active, was essential 
in successful and scientific manuring. They also 
found that these lime compounds in the surface 
soil served a further important use by preventing 
the soluble silicates being taken up by the root? 
of the plant, as these soluble silicates were taken 
up by the lime, and still more readily by the 
magnesium obtained from the lime, and then 
formed insoluble silicates which were retained 
in the soil, and did not difiuse into the 
plant, 80 that there was produced a non-sili- 
cated stem, or in the other words a cellulose 
stem, which would bend without breaking in 
the wind, while the non-silicated straw was 
much superior in value to the silicated straw. 
They ridiculed the old idea that »olubIe silica 
built up in the tissue of the plant gave .strength 
and solidity to the stem, and thej' pointed out 
that silica was, to all intents and purposes 
glass, so that straw with a backbone of silica 
was a brittle substance which was very liable 
to be broken and lodged by the wind, and 
moreover was of very inferior feeding value. 
They also found that just as in the manufac- 
ture of beer or whi«ky, or in fact in any 
process of fermentation, grei.t quantities of car- 
bonic acid were produced, so through the opera- 
tions of the soil ferments great quantities of 
carbonic acid were produced in the soil, and 
one great function of subsoil drains was to 
provide an outlet for the great amount of 
carbonic acid produced in the soil through the 
operation of the soil ferments. The same line 
of reasoning went to show that the commonly 
accepted doctrine as to capillarity required to 
be recast, and in fact that the whole of the 
old system of agricultural science as taught in 
the text-books commonly used, required to be 
pulled down and built up anew on a biological 
basis. 
{To be concluded-) 
THE SOLUBLE MINERAL MATTER OF SOILS, 
By Thomas H. Means, 
Assistant in Division of Soils U.S. Department 
of Agriculture. 
If a piece of granite be exposed to the weather 
for along time, changes will be noticed gradually 
taking place. The rock will whiten and finally 
fall to pieces, leaving a coarse powder without the 
slightest resemblance to the original rock. If the 
rock is weighed, it will be found that some of the 
material composing the rock has disappeared. 
This process of the breaking down of rocks has 
been going on forages unnumbered, and to-day 
nearly all of the rocks are covered with a layer of 
rock pov>fder or soil. While tlie rock is breaking 
down, or weathering, as it is termed, masses and 
lichens begin to grow, and, as they die and give 
place to other plants, their remains decay and 
leave in the decomposing rock the black coloring 
matter which is called organic matter, ana which 
in certain stages of decomposition is called humus. 
When the rock is all broken down and the organic 
matter, together with the humus, is mixed with the 
rock powder, there remains what is termed a soil. 
Many chemists haved studied this weathering of 
rocks and the formation of soils, and all of them 
agree that in the process huge quantities of the 
materials in the rocks are so changed by the 
weathering that they are rendered more or less 
soluble in water ; then as the rainfall penetrates 
the rock and the rock powder, this soluble matter 
is gradually dissolved and washed out, accounting 
for the loss in weight of the decomposing granite. 
Dr. George P. Merrill, of the United States 
National Museum, has examined a large number 
of rocks and soils, and has determined that rocks 
lose by solution from 10 per cent to as much as 98 
per cent of their weight in passing from the solid 
rock to soil, that is to say. in the formation of ixv. 
acre of soil one foot deep from 200 to 86,00J toiii 
of thi rock are removed by solution, 
