122 
Spratt . — The Morphology of the Root Tubercles of 
for two days, at the end of which period a normal healthy culture had 
been produced only in the medium inoculated from the culture containing 
the larger spherical organisms. These bodies appear to be analogous with 
the so-called ‘ bacteroid ’ forms produced by other species of Pseudomonas 
radicicola , since by inoculating freshly prepared media with them the 
small typical bacilli are formed, which subsequently give rise to them 
again. 
The above data indicate that the organisms living inside the root 
tubercles of these two non-leguminous plants are morphologically identical 
with Pseudomonas radicicola , which inhabits the tubercles of leguminous 
plants. An attempt was made to determine also their physiological capa- 
bilities with regard to the assimilation of atmospheric nitrogen in the 
following experiments : 
Into each of two Erlenmeyer flasks, 400 c.c. capacity, was placed 100 c.c. 
distilled water, 1 grm. saccharose, 0-5 grm. potassium hydrogen phosphate, 
0*02 grm. magnesium sulphate. To one of these flasks, the control, was 
added 2 c.c. of a culture obtained from Alnus as described above. Both 
were then autoclaved and subsequently neutralized with sodium hydrate. 
The other flask, after cooling, was inoculated with 2 c.c. of the same culture 
as the control, and both were incubated at 25 0 C. for ten days. During 
this period the control remained apparently unaltered, but in the one con- 
taining the living organisms there was a visible change as described above. 
The nitrogen content of both flasks was determined by the Kjeldahl 
method of analysis. 
The following results have been obtained with cultures from Alnus and 
Elaeagnus respectively : 
Nitrogen founa 
in control. 
Nitrogen found 
in culture. 
Alnus 
Elaeagnus 
o-47 mg. 
0.62 „ 
o-45 » 
3.96 mg. 
3-85 » 
3-o7 „ 
3-32 „ 
Gain in Nitrogen 
due to organisms. 
3-49 mg. 
3*23 „ 
2.62 „ 
2-5 » 
The increased nitrogen content can only have been produced by 
the growth of the living Bacteria introduced, and must have been derived 
by them from the atmosphere. Every precaution having been taken 
to exclude all other organisms except those derived from the tubercles, 
these experiments demonstrate that the root tubercles of Alnus and 
Elaeagnus , like those of leguminous plants, assist in the assimilation of 
atmospheric nitrogen, and this explains how, as Hiltner observed, the plant 
benefits from the presence of these tubercles on its roots. 
The root tubercles of Alnus and Elaeagnus are usually present in 
clusters (PL XIII, Figs. 1 and 2), which may in Alnus attain a diameter of 
three inches or even more, but in Elaeagnus they are rarely more than an inch 
