28 
Noktii Carolina Agricultural Experiment Station 
Due to tlie large experimental error involyed'in the dilution plate method 
and in counting the plates, the numbers of bacteria in these tabulations are at 
best approximations. Changes in reaction in any of the media during the 
short period covered by the experiment were insignificant and in no way con¬ 
tributed to modify the rate of growth as will be apparent in studies to be re¬ 
ported in subsequent pages. In general, it will be seen that the different or¬ 
ganisms react similarly to the influence of initial reaction. There is a broad 
zone of pH within which the rate of cell multiplication is fairly uniform. This 
is entirely in accord with the findings of Cohen and Clark (10) with B. coli. At 
the'borders of this zone, near the critical acid and alkali limits, however, there 
is a marked effect. Were one to plot a curve showing these points, using the 
average generations per hour as ordinates against pH as abscissae, this curve 
would he essentially a straight line until the borders of the zone are reached 
in which region, between the maximum values which permit growth and the 
minimum values which inhibit growth, there is an abrupt slope to the curve. 
In the case of the several plant patliogenes, the character of the curve there¬ 
fore is quite like that of B. coli (10), in showing that the chief effect of re¬ 
action seems to be confined to the limiting H and OH extremes. These bor¬ 
ders vary with the different organisms, as has been demonstrated in a previous 
paper (23.) 
One other point of special interest is indicated also in Table 1 but can best 
be shown by a summary such as is presented in Table 2. 
Table 2.— Generations per Hour Within Definite pH Zones 
Organism 
4 
pH Range 
Average 
Generations 
per Hour 
% 
Bacterium glycineum - _ __ __ __- 
5.4 — 8.4 
5.4 — 8.4 
5.4 — 8.4 
5.4 — 8.4 
5.2 — 8.5 
5.4 — 8.5 
.36 
.37 
.23 
.37 
.47 
.44 
Bacterium sojae _ __ - __ _ 
Bacterium campestre . . _ _ _ - .. . _ _ 
Bacterium angulatum - - - _ _ _ 
Bacterium tabacum ... .. . . __ _ 
Bacillus carotovorus .... . ..... 
The average number of generations per hour, of these several organisms, 
within their range of growth is seen to be small when contrasted with such 
organisms as B. coli and B. aerogenes whose rate of growth was found by 
Cohen and Clark (10) to he 2.5 and 2.7, respectively, during their period of 
logarithmic increase. It should he remembered in this connection that these 
last named organisms can produce vigorous fermentation, whereas these plant 
parasites, as will he shown later, are all relatively slow acting. Whether or 
not there is a parallelism between generation time and rate of fermentation 
remains to be determined. Cullen and Cliesney (11) have shown a close re¬ 
lationship between the rate of cell multiplication and acid production by pneu¬ 
mococcus in plain broth. Their data show that a rise in the growth curve 
slightly precedes the rise in acidity. Quite different results however were se¬ 
cured by Jones (14) with pneumococcus in glucose broth. His curves show 
a sharp rise in number of cells at the fourth or fifth hour with a delay of 
seven hours in the onset of the period of acid production. 
