104 BACTERIA IN RELATION TO PLANT DISEASES. 
mung’s bacterioiden,’”’ and (3) bladder bacteroids. The third form occurs where the bacteria have 
multiplied enormously. The hemmung’s bacterioiden occur outside of the bacteroid tissue in nearly 
all the outer cells of the nodule, and not rarely in the normal bark of the root. 
Beyerinck found that the nodules did not develop on the roots of plants grown in sterilized soil. 
Frank reached the same conclusion in 1879, Hellriegel and Wilfarth in 1886, and Ward in 1887. 
Plants in soil rich in humus are sometimes free or nearly free from nodules. 
According to Beyerinck there is only one bacterial species, but not all the forms are identical. 
There are varieties. There is, for instance, a distinct difference between the bacteria occurring in 
Vicia, Ervum, Trifolium, and Pisum, on one hand, and in Lotus, Lupinus, Ornithopus, and Phaseolus 
on the other hand. In the large rapidly growing colonies one is most apt to find B. radicicola like 
ordinary bacteria; in the small 
slow growing ones there are more 
branched bacteroids. 
He obtained the strongest 
growing colonies out of the very 
young nodules, or out of the outer 
meristematic zone of the older 
ones in Vicia faba, this being the 
plant he studied most carefully. 
The inner zone of the meristem 
yielded more bacteroid elements 
and slower growing colonies. 
Thesame result was obtained with 
Lupinus polyphyllus. This he 
says is the lupin in which 
Woronine first saw the bacteria. 
The nodules of this plant are 
very large and the swarmers in 
them are very minute. ‘There 
are no slime threads and there 
is no meristem. 
The large watery colonies 
consist of a mixture of rods 
and swarmers, many motile. 
The rods exclusive of some long 
forms are about 4X1. The 
bacteroids of Vicia faba are some- 
what larger and average 5X 1. 
The swarmers are very small: 
Taken from Vicia faba they are 
0.9X0.18". They are so small 
that'granting them some plasticity 
they might easily penetrate the 
pericambium cells without leav- 
ing any visible wound. ‘They 
possessone polarflagellum. ‘This 
was inferred from behavior during slow motility rather than actually seen. Motility ceases almost 
immediately in hydrogen or carbon dioxide. The little slow-growing colonies also contain swarmers. 
B. radicicola has no special powers of fermentation, oxidation, or reduction. It does not produce 
spores. It is not harmed by freezing or drying (see fig. 35). Neither diastase nor invertase are 
produced. Cellulose and starch are not converted. Nitrates are not reduced. Oxygen is liberated 
from hydrogen peroxide. Itis aerobic. It does not liquefy gelatin. Meat-water peptone gelatin is 
too concentrated for the first cultures (isolations). ‘The addition of 0.25 per cent asparagin is useful 
in agar cultures. Cohn’s solution is too acid for B. radicicola. It will not grow in it even after 
neutralization. Aklaline and neutral solutions are also injurious. For B. radicicola from Trifolium 
repens 0.6 per cent af malic acid is useful. 
*Fic. 34.—Planar enlargement of stained section from a small root-nodule on soy-bean. Great bulk of section 
consists of cells much enlarged and ,eccupied by enormous numbers of Bact. leguminosarum. Colorless spaces between 
are occupied by smaller (non-distended) cells free from infection and bearing normal nuclei. Surrounding this central 
mass is vascular tissue and beyond that cortex (both free from bacteria). 
