4 -PHYTOLOGY AND THERAPEUTICS. 89 
sion that plants do not assimilate free nitrogen. This stimulated further investi- 
gations, the results of which tended to strengthen confidence in the view that 
these tubercles were the result of the irritation, or stimulation, of some soil 
organism, but as to the character of this organism there were many diverse 
opinions. In 1885 Brunhorst came forward with a paper in which he maintained 
that root tubercles were not caused by organisms but were normal structures. 
This view received the indorsement of others, and, for a time, shook the confi- 
dence in the theory that micro-organisms were the cause of root tubercles. Even 
Frank forsook his former conclusions. So at the close of what Atkinson calls 
the second, or middle, period of investigation (about 1886) the etiology of the 
whole subject still ‘‘ hangs in the balance.”’ 
Recent [nvesticatrons.— In 1887 Marshall Ward published the results of a 
very careful series of experiments in which he proves that root tubercles are 
caused by some kind of a soil organism, and this view is supported and confirmed 
by such investigators as Hellriegel, Wilfarth, Lawes, and Gilbert. Some authors 
give Hellriegel the credit of being the first to discover the true function of root 
tubercles. 
Doctor Salfeld was the first to experiment with this discovery under field con- 
ditions, and found that it was possible to increase the number of tubercles on a 
leguminous plant by inoculation. In 1888 appeared a valuable contribution by 
Beyerink, in which he names the bacteria causing these tubercles ‘‘ Bacillus ra- 
dicicola.’’ In the same year appears an article by Vuillemin, in which he agrees 
with those authors who call the organism a symbiont, but disagrees with others 
as to its nature. A. Prazmowski, in 1888, claimed that tubercles were the result 
of a parasitic fungus, but ina year or two later maintained that they were caused 
by bacteria. This later view was supported by others, as Delphino, Mattei, Lau- 
rent, and Frank, the last in 1890 partially returning to his former views. 
One of the first records of an American author in connection with this subject 
is that of Schneider, who, in 1892, published an article on the bacterioids of 
several species of leguminous plants. In 1891, F. Nobbe, E. Schmid and L. 
Hiltner investigated the physiological meaning of root tubercles on non-leguminous 
plants. Nobbe and Hiltner are also the originators of what is known as *‘ pure 
cultures.’’ - They have isolated the bacteria for seventeen different leguminous 
plants and are now able to grow these artificially. This discovery was first an- 
nounced before a German agricultural society February 19, 1896. They now 
prepare these bacteria on a commercial scale and sell them in bottles under the 
name of *‘Nitragin.”’ Geo. W. Atkinson of Cornell University, formerly of Ala- 
bama, has published in the Botanical Gazette for 1893 (Vol. 18) a history of the 
subject, together with some original work he carried on while in Alabama. He 
takes up the biological phase of the subject and gives some plates illustrating the 
manner in which the bacteria infect the root. Atwater, Woods, and Kedzie have 
also done some work along the same line. 
From what has been published on the subject it is clear that all the problems 
connected with the assimilation of free nitrogen, through the intervention of root 
tubercles, have by no means been solved. Even the best authorities seem to dis- 
agree on some of the most vital points. However, it is pretty well settled that 
the tubercles are the result of a micro-organism; but it has been proven that the 
organism producing tubercles on the pea or bean will not produce tubercles on 
clover and alfalfa, and vice versa. Whether these organisms are different species 
for different plants, or a modification of the same species, is yet a disputed ques- 
tion. Again, as the organisms attack the root, it is supposed that they exist in 
the soil, and the question would naturally arise as to whether they could be trans- 
