Studies on Physiology of Some Plant Pathogenic Bacteria 
11 
It will be noted that the results are in general accord with those on indica¬ 
tor media in that Nos. 268 and 269 are able to form acid from each of the su¬ 
gars, whereas Nos. 211, 270 and 19 form acid from dextrose and saccharose 
alone. 
Fermentation tubes. Sterile fermentation tubes were filled under 
aseptic conditions with sugar broths. The dissolved oxygen gas was not 
driven off, but it is not apparent that such a procedure is of value since it re¬ 
mains to be proven that heated broths do not again take up oxygen on cooling. 
The several strains have given similar results with heated and unheated tubed 
broths. No turbidity developed in the closed arm in seven-day old cultures, 
thus indicating that the organisms are strictly aerobic. Other organisms may 
of course react differently, but the dispelling of dissolved oxygen is apparently 
a factor of less importance than the agitation given fermentation tubes in 
handling them during examination. Slight agitation may cause apparent 
growth in the closed arm in the case of all strains so that it becomes easily 
possible to misinterpret the oxygen relation through the use of fermentation 
tubes. 
Character of colonies. It was only by increasing the percentage of agar 
above that which the writer was accustomed to use that it was possible to 
duplicate the appearance of colonies with respect to margin, contour and sur¬ 
face markings shown in Plate XV of Miss Coerper’s paper. While it has long 
been known that the density and viscosity of media exert a profound influence 
upon the character of the colonies (2), the importance of these factors has been 
largely overlooked in studies involving the cultural characters of bacteria. 
In the case of the soybean organisms, the differences in the character of the 
margins in 1, 2, and 3 per cent nutrient agars which were alike in all other 
respects are shown in figure 1. It will be seen that the margin of the colony 
becomes more uneven as the density and viscosity increases. Size, elevation 
and surface markings are also profoundly modified. 
Fig. 1.—Variation in the margin of colonies of Nos. 269, 211 and 19. When 
grown on 1, 2, and 3 per cent nutrient agar, as seen under the high 
power. 
DISCUSSION 
By avoiding the heating of media after the addition of the sugar, one pre¬ 
vents the reaction between the amino groups and the sugar with the resultant 
