205 
normal culture soil solution and the other in sterilized culture soil 
solution the former developed tubercles, the latter not. 
11, A period of dwarfed growth was noticed after inoculation 
with the culture fluid. 
12. During this period tubercles kept on developing. 
13. In soil free from nitrates active growth began only after 
the formation of tubercles. 
Hellriegel’s final summing up is as follows : 
1. The Leguminose have another source besides the soil from 
which to draw free nitrogen. 
2. This second source is the free nitrogen of the air. 
3. The plant itself has not the power to assimilate this free 
nitrogen, 
4. Active micro-organisms perform this function for the plant. 
5. The tubercles stand in intimate relations with the free 
nitrogen assimilating power of the Leguminose. 
In 1890 Frank wrote an article entitled ‘‘ Pilzsymbiose der 
Leguminosen” in which he not only verified Hellriegel’s conclu- 
sions, but also studied and described the micro-organisms con- 
nected with this nitrogen-assimilating function. His conclusions 
may be briefly summed up as follows : 
I. Some Leguminosz live in symbiotic relations with a very 
simple fungus which infects the plant as soon as it begins to 
develop. 
2. This fungus belongs with the smallest organisms. It is 
One of the Schizomycetes, the Rhizobium leguminosarum. 
3. It very likely develops and multiplies in the soil. It is 
Present in all natural soils, at least to some extent. 
4. Roots of the Leguminosae have the property of excreting 
4 peculiar substance which attracts the spores of the fungus. 
Some of these spores develop on the outside of the root, others 
are conducted into the interior of the root tissue by peculiar pro- 
toplasmic strands built up by the normal cells of the plant 
(/nfektionsfaden). : 
5. The fungi combine with the protoplasm of the cells, forming 
a mixture called “ mycoplasm.” The fungus may be found in 
nearly all parts of the plant, even in the seed. A new plant may 
be infected from the spores in the embryo. 
