70 Orr—L&ar GLANDS oF DioSCOREA MACROURA., 
of just over 100, while a medium of a different composition, and 
a higher initial nitrogen content, showed a gain of only 67 per 
cent., although, in the latter experiment, the culture had been 
maintained over a much longer period of time. 
The power of nitrogen fixation possessed by the Duoscorea 
organism was tested up to fully 80 days after inoculation, but its 
effect on the nitrogen content of artificial media is typified by 
the following result, obtained by the Kjeldahl analysis of a 23 
days culture growth. 
Nitrogen Content in roo grams of Culture Medium. 
In the control, 23.18 mg. 
In the apes medium at con- 
clusion of experiment, 48.61 mg. 
Gain, 25.43 mg. 
The increase in the nitrogen content may appear small when 
contrasted with the results obtained from similar experiments 
carried out with nitrogen bacteria from root-tubercles. It com- 
pares not unfavourably, however, with some of Faber’s 
estimations of the nitrogen increase in culture solutions, brought 
about by the organism isolated from Pavetta Zimmermanniana. 
He found that, with a nitrogen content of 12.256 mg. in the 
control, the gain in three separate experiments was, respectively, 
9. mg., 19.592 mg. and 12.750 mg. of nitrogen per 200 Cc. 
of culture solution. ‘The duration of each experiment was 20 
days. Using an almost nitrogen-free culture solution, Faber 
found that the increase in nitrogen, for the same length of time, 
was much greater than the amounts quoted above, while with a 
higher percentage of nitrogen in the control, the increase was 
correspondingly less. 
That the bacterium found in the glands of Dioscorea macroura 
stands in the same relationship to the plant, as do those 
organisms, described by Faber and Miehe, to the plants with 
which they are allied, is an interesting hipothesiw. which gains 
support from the behaviou? of the isolated bacterium in culture 
media. But whatever powers of nitrogen-fixation may be 
possessed by the organism, when divorced from the plant, it is 
quite another matter to state categorically, that, within the plant, 
the bacterium plays the réle of nitrogen provider, in the same 
way as do the bacteria in root-nodules, although the high 
soba oue content of the acumen does seem to postulate a certain 
activi 
It may be merely a case of contingent symbiosis, or a fortuitous 
_ association, such as that mentioned by Koorders* in his 
description of the ‘‘ wasserkelche’’ of tropical plants. 
S, H. Koorders in Ann, Jard. Bot. Buitenzorg, xiv. (1897), p. 451. 
_— 
