996 The American Naturalist. Denai : : 
tain species of bacteria, or at least certain species of micro- — 
organisms, these micro-organisms crawl into the roots of the a 
pea, and then begin to multiply inside the roots. The little 
roots begin to swell and there appear upon them a lot of min- — 
ute nodules, which have received the name of “root-tuber- — 
cles.” If I am not mistaken some of those little root tubercles — 
were shown to the meeting here last evening. These root — 
tubercles, as I say, make their appearance, and it is found that — 
wherever these root tubercles do make their appearance the — 
plant gets hold of nitrogen and grow well. Where these root 
tubercles do not make their appearance the plant is unable to — 
get hold of the nitrogen unless it is fed to them. Now these — 
root tubercles are produced by bacteria, and these root tuber — 
cles are the agencies by which, in some as yet unexplained — 
way, the pea gets nitrogen out of the air. S 
Thus you see that in the final analysis of the life of a plant, 
in the assimilation of nitrogen from the air, we are brought to — 
the conclusion that it is the agency of these minute micro — 
scopic organisms that is the source of the assimilation d 
nitrogen from the air by plants. Thus we owe the growth of - 
these plants to bacteria. How the bacteria get the nitrogen — 
out of the air has not yet been explained. a 
Even before the scientists made this discovery the farmet 
had made the discovery practically on his farm. You have 
known that you could in some, to you inexplicable, way reju 
venate an old, worn-out soil by cultivating clover upon ip 
by cultivating beans. That has been the practice of farmers ; 
for years. It has been found that in some way the lt : 
of clover, instead of exhausting your soil as the cultivation M 
some plants does, really increases the fertility of the soil. 
You cultivate your clover for one season, then the next seas” 
you plow the roots into your soil, and you find the field 
produce a better crop than before. This result is brought 
through the agency of these organisms. The clover bel 
to the family of peas, and clover is one of the pl 
particular species of bacteria that I am speaking of can 
The bacteria in the soil get into these roots, grow 1 
produce these root tubercles, and by means of these the ¢ 
