Orr—LEAF GLANDS OF DIOSCOREA MACROURA. 69 
inducing it to grow in a Buchner’s tube, over strong pyrogallic 
acid in caustic potash. Liquefaction of gelatin was brought 
about after a comparatively long period of growth, ranging from 
18 to 28 days, the liquefied gelatin subsequently becoming 
cloudy. Sterilised milk, to which a culture of the bacterium had 
been added, ultimately became clear and translucent, and gave 
a slightly acid reaction with litmus. The transference of a dro 
of this fluid to nutrient gelatin resulted again in the production 
of a pure culture of the organism 
In suitably stained sections ra the glands of Dioscorea 
macroura, relatively large, irregularly shaped bodies, resembling 
the bacteroids of leguminous nodules, had been observed, and 
these also appeared in the cultures on artificial media. Similar 
involution forms were found by Faber* in the bacterial leaf- 
glands of Pavetta and Psychotria. "This author carried out an 
extended research on the physiological attributes of the organism 
inhabiting these ‘‘bakterienknoten,’’ and, as a result of his 
experiments, he came to the conclusion that the ‘‘ mycobac- 
terium,’’ isolated from the glands, possessed the power of 
utilising free nitrogen, and that the inter-relationship of plant 
and micro-organism. was therefore of the nature of a 
“ bakteriensymbiose..’ 
A similar view of the intimate relationship existing between 
Ardisia crispa and its associated bacterium was expressed by 
Miehe, after a lengthy series of observations on the biology of 
the micro-organism and its effect on the growth of the plant. 
In the light of these researches, and having regard to the 
several points of resemblance between the glands of Dioscorea 
macroura and those of other tropical plants investigated by Faber 
and Miehe, it was essential that the Dioscorea organism should 
be subjected to similar tests, in order to determine whether, or 
not, it was endowed with like properties, and capable of bringing 
free nitrogen into combination. Kjeldahl] determinations of the 
nitrogen content of cultures of the bacterium, isolated from the 
glands, were therefore compared with similar estimations of the 
amount of nitrogen present in the culture medium in sterile 
controls. In every case, there was evidence of an appreciable 
gain in the nitrogen content, presumably due to the activities 
of the organism. 
he percentage increase in nitrogen varied according to the 
nature and composition of the medium employed, and seemed 
to be inversely proportional to the amount of combined nitrogen 
present in the nutrient medium at the time of inoculation, e.g 
a nutrient medium with a low initial nitrogen content, three 
weeks after inoculation, showed a percentage increase in nitrogen 
* F.C, von Faber in Jahrb. fiir wiss, Bot. li. (1912), p. 283, and liv. (914), p. 243. 
