Apr.. 1922] HOPKINS — HYDROGEN-ION CONCENTRATION 
165 
conidial production or perhaps segmentation of the mycelium. In the less 
acid cultures a single colony was usually formed from the original inoculum. 
At the end of the fourteen-day period (fig. 4) a depression is still present 
but it is not so noticeable. At this time the growth curve resembles some- 
what the growth curve obtained by Meacham (7) with wood-rotting fungi. 
Fig. 4. Hydrogen-ion concentration and growth of G. Sauhinetii on Hquid media- 
phosphate series after fourteen days. 
Experiment 3. Growth on a Solid Medium— Lactic-Acid Series 
The growth of the organism was also studied on potato-dextrose-agar 
plates of varying hydrogen-ion concentration. Lactic acid was used in 
adjusting the reaction as follows: to 20-cubic-centimeter portions of the 
melted medium a varying number of drops of lactic acid (50 percent by 
volume) was added and petri dishes were poured. A separate series of 
tubes was prepared in the same manner and used for the hydrogen-ion 
determinations. Each plate was inoculated in five or six places with the 
mycelium of Gibberella Sauhinetii on small blocks of agar, and the plates 
were incubated at 25° C. At the end of 21 and 44 hours respectively, 
measurements of the diameter of the colonies in millimeters were made. 
The results at the ends of these two periods are shown in table 3 and repre- 
sented graphically in figure 5. The diameter given is the average diameter 
of all the colonies on a plate. 
Table 3. Hydrogen-ion Concentration and the Growth of Gibberella Saubinetii on Potato- 
Dextrose Agar in which the Rea ction was Adjusted by Means of Lactic Acid 
Drops of Lactic 
Acid per 20 Cc. 
of Medium 
Ph 
Average Diameter of 
Colonies after 
21 Hours (Mm.) 
Average Diameter of 
Colonies after 
44 Hours (Mm.) 
0 
6.9 
18.2 
41.2 
I 
4-5 
137 
32.6 
2 
4.0 
10.4 
25.6 
3 
3-8 
9.4 
21.0 
4 
3.6 
1-7 
10.6 
