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 uame of Pseudomonas syringce, a being van Hall's own isolation and b 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 aniins, 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 the}' 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., XXVI.) 



PIGMENTS. 



Bacterial growths are often bright colored, and an examination of the pigments 

 should form part of one's study of an 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. g., near the maximum or 

 minimum temperature ? Bacillus prodigiosiis 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, benzole, 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 (Mcdicago dctiticitlala Willd.) and 

 ther U-uminous Plants. Proc. Calif. Acad. Sci., 3d series, Botany, Vol. II, No. 10, San 

 Francisco, Cal., .Turn- 21, 1902, pp. 295-328, with I plate. 



