March 1, 1904. j Supplement to the Tropical AgricuUv/rist." 
645 
Saxon hills, some half-hour's ride by railroad from 
the city of Dresden. Here is located the Forest 
Academy of the kingdom, with which Profess jr 
Nobbe is prominently connected, and he^'e also is 
the agricuUurnl experiment station of which he is 
director. He lias been for more tii in forty years 
the editor of one of the mo<t iinportant scientilic 
publications in Germany, he is chainnati of the 
Imperial Society of Agricultural Station Director.'', 
and he has been the reci[)ient of many honours. 
But the greatest of all his work is his remark- 
able discovery of a method of inoculating the soil 
with bacteria to make it yield richly where it lay 
barren before. In times past investigators of soil 
and plant culture demoted their attention largely 
to studying the composition of various kinds of 
soil, to the improvement of fertilisers, and in 
suggesting new systems of drainage and water- 
supply. I'rofe'^sor Nobbe has gone a step farther 
in advance, declaring that plants will grow, vmder 
certain conditions, just as well without soil as 
with soil. At first glance this may seem strange 
enough, yet here are trees, from eight to 10 inches 
in circumference at the base of the trunk, growing 
in clean water, without a sign of soil of any 
description. They stand in rows just back of the 
Forest Academy and near Professor Nobbe's green- 
house. Bach tree is suspended in a large glass 
Jar surrounded by a green-painted case. When 
this case is opened one may look through the glass 
and see the roots of the tree hanging there in the 
clean water. The oldest of the trees was planted, 
or rather the seed was immersed in water, in 1878, 
and it has grown to full size without even touching 
soil. Leaves and blossoms have come in the spring, 
and in the winter the water and the roots have 
frozen solid all these years, and the tree still 
thrives. Indeed, some of its seeds were immersed 
in water, and the trees of the second generation 
have been grown to considerable size. Then their 
seeds were immersed, and there are now growing 
small trees three generations removed from the 
soil — certainly a clear proof of Professor Nobbe's 
assertion that actual contact with soil is not 
essential for plant growth. In order to produce 
such results, however, it was necessary to keep the 
trees supplied with artificial food. This Professor 
Nobbe prepared in his laboratory — -a certain 
definite amount of chlorate of potash, sulphate of 
magnesium, phosphate of iron, phosphate of 
potassium, and a nitrate. A small quantity of 
this mi.vture was dissolved in the water of the jars 
every four weeks, and thus the trees have been 
kept flourishing all these years, showing that 
there was no element in the soil necessary to plant 
growth that man could not manufacture at will. 
Nor was this all that the experiment showed. 
Professor Nobbe knew to the last gramme how 
much food he had given to the plant through the 
water; he also knew that the water before adding 
the chemicals named was absolutely pure ; yet 
when he came to analyse some of the plants thus 
grown he found that they contained much greater 
^ . quantities of various elements than he had supplied 
through the water. This constituted a proof 
positive that the plant drew largely upon the air 
for its nourishment — a fact well-known to science, 
but uot before positively and (juautitatively 
demonstrated. The proportion of substance drawn 
from the air was found to be very large. It is 
said that of every one hundred pounds of wheat 
harvested from our fields barely one pound is 
actually drawn from the soil, the remainder 
coming from tlie free air and the wa'er. And yet 
the effort to su])plv this one-one-hundredth of the 
plant's food has caused most of the wars and 
conflicts of the world, has led to the discovery 
and settling of new continents, and forms to-day 
the foundation of commerce and .finance. 
As soos as science had convinced itself of the 
great truth that plants are fed largely from 
substances in the air, it began at once to study 
the problem as to how the plant is able to appro- 
priate this aerial food. The chief chemical 
elements in all vegetable substances are oxyen, 
carbon, hydrogen, and nitrogen. Added to these 
are small quantities of potassium, phosphorous, 
iron, sulphur, magnesium, and calciunl. Of all 
these elements the only ones about which there is 
any difficulty are nitrogen, potassium, and 
phosphorous. The others the plant obtains with- 
out difficulty, but the supply of nitrogen, especially, 
too often runs short. When land is said to be worn 
out, the meaning is that the supplies of nitrogen, 
potassium, and phosphorous have been exhausted 
bv too constant cropping, by taking much away 
from the soil and returning nothing to it. 
Manure and fertilisers which are rich in these 
lacking elements, especially those which, like barn- 
yard manure, are rich in nitrogen, are thus applied 
to the land, thereby restoring its producing capa- 
bility. Nitrogen is the all-importaht element. 
Potassium and phosphorus are usually present iu 
abundance, or they can be easily supplied in the 
form of wood-ashes and other fertilisers, but 
nitrogren is more expensive and more difficult to 
restore. Nitrogen is what makes the muscles and 
brain of a man, it is the essential element of all 
elements iu the growth of animals and plants; and, 
significantly enough, it is also the chief consti- 
tuent of the gunpowder and other explosives with 
which the war-s of the world are waged. A single 
discharge of a 13-inch gunliberateseuough nitrogen 
to produce many scores of bushels of wheat. 
This fact may become, in the future, a greater 
deterrent of war than we can now imagine. 
The failure of the nitrogen of the soil and the 
inability to supply it to sufficient quantities by 
artificial means has formed the basis of the 
predictions of coming starvation made by Sir 
William Crookes and others. Indeed, if the 
world ever starves it will be from lack of nitrogen; 
and yet if such starvation takes place it will be in 
a world full of nitrogen. For there is not one of 
the elements more common than nitrogen, not one 
present arouud us in larger quantities. Four-fifths 
of every breath of air we breathe is pure 
nitrogen — four-fifths of all the earth's atmosphere 
is nitrogen. If mankind dies of nitrogen starvation, 
it will die with food everywhere about it and 
within it. 
But, unfortunately, plants and animals are 
unable to take up nitrogen in its pure form as it 
appears iu the air. It must be combined with 
nitrogen iu the from of ammonia or in some nitrate. 
These facts have been well l^uowa to science for 
