155 
But in spite of all of these precautions it was not always possible to 
prevent the penetration of foreign organisms to the tubercles. In a 
certain number, however, of the successful experiments in which the 
bacteria alone remained in contact with the roots the results obtained 
were identicat with those obtained by Hellriegel and Wilfarth. 
There was a fixation of nitrogen in all the pots in which the bac- 
teria were sowed, and in those only. 
Thus in a sterile soil, without microbes, a pea containing 12 milli- 
grams of nitrogen produced only 1.166 grams of dried crop, in which 
13.2 milhgrams of nitrogen were found, or about as much as was con- 
tained in the seeds sown. Where microbes were present, on the con- 
trary, the dried crop weighed 3.544 grams and contained 82.6 milli- 
grams of nitrogen. Therefore the bacteria had given to the plant 
the faculty of taking from the air 70 milligrams of nitrogen inde- 
pendently of all other microbic intervention and under the same 
exterior conditions. 
By using water in the place of sand Prazmoftski also obtained the 
same results. Some peas grown in a nutrient solution without nitro- 
gen and sterilized gave only 9 milligrams of nitrogen, whereas others 
grown in a similar liquid but supplied with bacteria gave from 26 to 
82 milligrams. 
These experiments then verify in the most complete manner the 
views of Hellriegel and Wilfarth; the fixation of nitrogen by the 
leguminosez is a consequence of their symbiotic union with an 
infinitely small organism whose germs are profusely scattered abroad 
and which enables these plants to grow sometimes with vigor without 
any artificial inoculation im soils destitute of all nitrogenous food. 
It was these germs which enabled G. Ville to first observe the 
fixation of atmospheric nitrogen by these same plants, and it was 
their irregular dissemination which caused the inequality in his 
experiments, and if Boussingault found it impossible to obtain the 
same results il was simply because he cultivated his plants under such 
conditions that they could not acquire sufficient vitality to profit by 
their union with these bacteroids. 
In effect at the beginning of vegetation in soils without nitrogen, 
but into which microbes have been introduced, an interval of stop- 
page of growth has been observed, so complete as to make us fear a 
rapid decay of the plant, and this period of intermission always 
coincides with the appearance of the tubercles on the roots of the 
plants. At this time the invading organisms derive their nourish- 
ment from the juices of the voung plant : they exhaust it, and if the 
latter has not the strength to resist this invasion, which then con- 
stitutes a sort of parasitism, if its roots are not able to develop freely, 
or, again, if its leaves remain in a badly ventilated atmosphere, 
always saturated with aqueous vapor, the plant will inevitably perish. 
If, on the contrary, it can resist, it will very soon gain the advan- 
tage; it then takes from the bacteria the nitrogenous matter which 
they contain and compels them to form more of it from the nitrogen 
which surrounds them. Doubtless on its side the bacteriod profits 
as much as the plant from its symbiosis; it is probable that it receives 
from the latier hydrocarbons—sugars or others—in exchange for the 
albuminoids which it gives to the plant, and thus it is that this union 
may exist until, finally, the moment arrives when the plant, having 
