64 BACTERIA IN RELATION TO PLANT DISEASES. 
Fig. 56 shows how differently quite similar-looking cultures may react when 
submitted to this test. Both of these organisms were received from van Hall under 
the name of Pseudomonas syringe, a being van Hall’s own isolation and 4 being 
supposedly a subculture from Beyerinck’s isolation. Neither one would produce 
any blight in lilac shoots. 
There is no simple way known to the writer of distinguishing ammonia from 
the amins, as both react to Nessler’s reagent. Nitrogen may be distinguished from 
the other gases of fermentation by the fact that it is not absorbed by sodium or 
potassium hydroxide and will not burn or support combustion. This gas is produced 
readily from nitrates by a number of green-fluorescent organisms (dung-destroyers) 
but not by all of them. 
FIXATION OF FREE NITROGEN AND THE OXIDATION OF AMMONIA AND AMMONIUM 
SALTS TO NITRITES AND NITRATES. 
These processes are probably common enough to organisms of the soil, many 
of which have not been investigated, but they are not known to be brought about by 
plant parasites exclusive of the root-tubercle bacilli of the Leguminosae, which some 
believe to be parasites (see Peirce).* They are believed to be of rare occurrence in 
bacteria which grow well on ordinary culture media. 
The nodules on roots of plants will hereafter be considered more fully. ‘The 
reader should consult a paper by Geo. T’. Moore on “ Soil Inoculation for Legumes,” 
Bureau of Plant Industry, United States Department of Agriculture, Bull. 71, Jan- 
uary 23,1905; and one by Maria Dawson, “Further Observations on the Nature and 
Functions of the Nodules of Leguminous Plants,” Philosophical ‘Transactions 
Royal Society of London, Series B, Vol. CXCIII, pp. 51-67, 1900, with 2 plates. 
ASSIMILATION OF CARBON DIOXIDE. 
Some soil organisms are believed to obtain their carbon directly from carbon 
dioxide, and would thus be exceptions to the law that all non-chlorophyllous plants 
must obtain their carbon from organic substances. ‘This supposition, while probably 
true, has not, we believe, been established satisfactorily. Its elucidation offers a 
most interesting line of research (see Bibliog., XX VI.) 
PIGMENTS. 
Bacterial growths are often bright colored, and an examination of the pigments 
should form part of one’s study ofan organism. ‘They may be considered as follows : 
(1) Under what conditions formed ? Can they be eliminated by growing the 
organisms in the dark or under unfavorable conditions, e. ¢., near the maximum or 
minimum temperature? Baczllus prodigtosus is a favorable organism for experiment. 
(2) In what soluble (water, hydrogen-peroxide in water, ethyl alcohol, methyl 
alcohol, glycerin, acetic.ether, petroleum ether, sulphuric ether, acetone, chloroform, 
turpentine, benzine, berizole, xylol, toluol, carbon bisulphide, etc.)? ‘The pigment 
should be tested in as many solvents as possible. 
*Peirce, George James. The Root-tubercles of Bur Clover (Medicago denticulata Willd.) and 
of Some Other Leguminous Plants. Proc, Calif. Acad. Sci., 3d series, Botany, Vol. II, No. 10, San 
Francisco, Cal., June 21, 1902, pp. 295-328, with 1 plate, 
