Studies on Physiology of Some Plant Pathogenic Bacteria 
47 
PREPARATION OF AGAR 
Since the agar content of a medium through its effect upon viscosity pro¬ 
foundly influences the character of the colonies, a description of colonies as a 
means of specific identification is of value only when the concentration of agar 
is known. This factor has been largely overlooked since too often media are 
designated as plain agar, bean agar, corn-meal agar, dextrose agar, etc., 
and are unaccompanied by any statement of their percentage composition. 
In the routine preparation of agar media, if the reaction is adjusted when 
they have been cooled to 50° to 60°C. and if vegetable or fruit decoctions are 
added at this temperature and they are not subsequently heated, there is no 
loss in jellifying power. The failure of such media as prune agar or rhubarb 
agar to solidify, an experience which many phytopathologists have encoun¬ 
tered, may by this procedure, be averted. Solid media may thus be rendered 
very acid and can be employed in studies in which only liquid media have 
heretofore been available. 
LITERATURE CITED 
1. Clark, W. M. The Determination of Hydrogen Ions. 317 p., 1920. 
2. Meacliam, M. R., Hopfield, J. H., and Acree, S. F. Preliminary note on 
the use of some mixed buffer materials for regulating the hydrogen ion con¬ 
centrations of culture media and of standard buffer solutions. Jour. Bact. 
5 : 491-499, 1920. 
3. Conn, H. J., et al. Methods of pure culture study. Progress report for 
1918 of the Committee on the Descriptive Chart of the Society of American 
Bacteriologists. Jour. Bact. 4: 107-132, 1919. 
4. Clark, W. M. The reaction of bacteriologic culture media. Jour. Infect. 
Dis. 17: 109-136, 1915. 
5. Conn, H. J., et al. Report of the Committee on the Descriptive Chart for 
1919. Jour. Bact., 5: 127-141, 1920. 
6. Conn, H. J. and Breed, R. S. The use of nitrate reduction test in char¬ 
acterizing bacteria. Jour. Bact. 4: 267-290, 1919. 
7. Brightman, C. L., Meacham, M. R., and Acree, S. F. A spectrophoto- 
metric study of the salt effects of phosphates upon the color of phenolsul- 
phonplithalein salts and some biological applications. .Tour. Bact. 5: 169-180, 
1920. 
