June 1, 1904.] Supplement to the "Tropical AgricuUwist." 
871 
that the bacteria tliemselves fix the nitrogen in the 
roots of the plant, and that it is then used as nitrates 
would be used from the soil. It is certain that 
these tubercle organisms can fix free nitrogen in 
cultui'es, and there is no reason to suppose that 
this power is lost when within the roots of a legume. 
Furthermore, ' it seems as though the plant 
actually uses the contents of these tubercles, for 
at the end of the season the tubercles are found to 
be much softer and shrunken, and are practically 
emptied of their mass of bacteria. 
It is a well-established fact, and has been 
shown by a number of independent investigators 
in various parts of the country, that the legumin- 
ous crops which bears tubercles will exceed a simi- 
lar crop without tubercles by from 100 to ], 000 per 
cent ; that is, a field of clover grown on such poor 
soil that it would only yield 200 pounds to the acre 
would be so invigorated by the presence of tubercle- 
forming bacteria that on exactly similar soil it 
would produce from 400 to 2;000 pounds to the acre, 
and this without any cost whatever for fertilizers 
and with very little more labor. la addition to 
the inciease of the actual weight of the crop, tuber- 
cles also cause the plants to flower and fruit earlier, 
and the number of seeds produced is very much 
greater. 
Thus it will be seen that it is worse than use- 
less to attempt to grow any leguminous crops 
without being certain of the presence of the bac- 
teria which enable the plant to fix free nitrogen. 
It would be much better to fertilize heavily and 
attempt to raise some more profitable crop than to 
introduce clover or beans or some other legume for 
the purpose of enriching the soil. It can not be 
too strongly emphasized that unless the tubercles 
are present the leguminous crop is of absolutely no 
more benefit to a soil than wheat or potatoes. 
While these organisms are pretty generally 
distributed throughout the earth, and it is quite 
possible in many parts of the country to grow 
almost any leguminous crop and secure these tuber- 
cles, it is also true that certain regions are practi- 
cally devoid of the right kind of bacteria, and that 
unless some artificial means of introducing the 
germs be resorted to the crop will be a failure. 
In the past there have been two methods used 
in attempting to bring about artificial inoculation. 
Naturally where a certain leguminous crop has 
been grown successfully for a number of years the 
soil will become filled with tubercle organisms, and 
by transporting this earth to wew fields the organ- 
isms will thus become available for forming the 
nodules in localities where they previously had 
not existed, Tliis was the means by which the 
soy-bean organisms were brought from Japan, and 
there are very few places in tliis country where soy 
is now grown that did not receive their inoculation, 
indirectly at least, from the Japanese soil. 
There are twoserious objections tosoil inocula- 
tions, however. One is the expense, for it requires 
anywhere from 500 to 1,500 pounds of earth per 
ncre to produce a satisfactory growth of tubercles, 
and if this has to be trausportted for a large farm, 
the cost is almost prohibitive. There is still ano- 
ther and more serious objection, however, and 
that is the danger of transmitting plant diseases 
by this method. Several of the more serious dis- 
eases which attack crops are readily conveyed in 
the soil, and there are numerous cases on record 
where diseases of leguminous and other crops 
have been introduced into regions previously 
entirely free from them through an effort to bring 
about a soil inoculation of the tubercle-forming 
organism. Consequently, if any safer and cheaper 
method could be devised for making these germs 
available, it would be most desirable. 
A few years ago certain German investigators 
put upon the market a product known as nitragin, 
which purported to be a pure culture of the root- 
tubercle organisms. These cultures were only 
adapted to specific crops, for it has been held that 
each kind of leguminous plant had a special germ 
better adapted to produce tubercles upon it than 
any other form, and for this reason it was neces- 
sary to use one organism for clover, another for 
peas, and so on. This preparation, nitragin, has 
been used with varying success abroad. Some ex- 
periments seemed to show that it was of the great- 
est value, while others were complete failures in 
demonstrating its worth. The failures so far out- 
numbered the successes, however, that its manu- 
facture has been abandoned, and it can no longer 
be obtained. A few attempts have been made to 
use these cultures in this country, and while some 
very satisfactory results were obtained, the number 
of failures was even greater than abroad, the vary- 
ing conditions involved in transportation and the 
length of time which elapsed before the germs 
could be used being fatal to about 80 per cent, of 
the material imported.* 
A little more than a year ago the investigation 
of these nitrogen-fixing bacteria was begun in the 
laboratory of plant physiology of the Bureau of 
Plant Industry, with the hope of discovering 
some method of artificially inoculating soils which 
were devoid of the proper organisms, and of insur- 
ing their producing the desired result. It was 
soon found that the method in use by the German 
investigators was not adapted to the life of the 
organism ; that is to say, the use of rich nitrogen- 
ous food material, such as decoctions of the host 
plant, were not calculated to produce an organism 
which would fix free nitrogen from the air. It 
was found that while the bacteria grew luxuriantly 
upon such media, they became less and less active, 
until eventually they lost completely this nitrogen- 
fixing power. It seemed as though the large amount 
of nitrates in the media upon which they were 
grown made it no longer necessary to draw nitro- 
gen from the air, and consequently they deterior- 
ated until they became of no more value than the 
common soil forms. It has been found, however, 
that by gradually reducing the amount of nitrogen 
in the culture medium it is possible to greatly in- 
crease the nitrogen-fixing power of these germs, 
and that by proper manipulation their activity 
may be increased from five to ten times that which 
usually occurs in nature. Pr.ictical field experi- 
ments have shown that of two cultures, one grown 
on nitrogen-free media and the other on a medium 
We ourselves have made trials with Nitragin, 
but without success. — Ed. A.M. 
