868 
Journal of Agricultural Research 
Vol. XXIV, No. lo 
fungus grew from a single experiment were made into one sample and 
immediately used for the maceration of raw sweet-potato disks. A 
portion of this solution which was first steamed to inactivate the enzym 
together with the uninoculated solution, served as controls. Hydrogen- 
ion determinations were made of the inoculated solutions and of the 
uninoculated controls at the close of the experiment. 
A good growth was obtained in each of the different series. The best 
growth and fruiting, however, were obtained when dextrose and pectin 
were combined in the same solution. 
Some interesting results with respect to the hydrogen-ion concentra¬ 
tions were likewise obtained. In one experiment Czapek’s solution 
plus 20 per cent dextrose with an original hydrogen-ion concentration 
of Ph 5.24 had a Ph of 1.93 after the fungus had grown on it for 4 days. 
When I per cent pectin alone was substituted for the dextrose the solu¬ 
tion had an original Ph of 4.38 and (after the fungus had grown upon it) 
a final hydrogen-ion concentration of Ph 3.76. 
In another experiment the following results were obtained: Czapek's 
solution plus 20 per cent dextrose with an initial Ph of 4.94 had a final 
Ph of 1.85. When 20 per cent dextrose and i per cent pectin were used 
the initial Ph was 4.09 and the final 1.70. If, on the other hand, pectin 
alone was used the original hydrogen-ion concentration was Ph 4 43 
and the final Ph 3.90. The results show clearly that the pectin itself 
while supporting a good growth of mycelium is not so efficacious in the 
production of acid as dextrose. 
Equally striking results were obtained with respect to the production 
of a middle lamellae dissolving enzym. It has already been pointed out 
that pectinase was not produced on Czapek's nutrient solution with 
dextrose as a source of carbon. Comparative experiments as detailed 
above showed that only a feeble macerating principle could be demon¬ 
strated either in the mycelium or in the solution on which the fungus 
grew when Czapek’s solution plus 20 per cent dextrose was used or when 
the same solution plus 20 per cent dextrose plus i per cent pectin were 
employed as the source of energy. On the other hand, when pectin 
alone was used as a source of carbon a vigorous cell wall dissolving enzym 
was secreted. In one series of experiments coherence of the cells of 
sweet-potato disks immersed in the solution was entirely lost in 3X kours 
when pectin alone was used. When dextrose was employed 24 hours 
were required. There was no maceration in 24 hours in the steamed 
control when pectin was used. When glucose was used maceration was 
completed in 24 hours, which was probably caused by the acid (Ph 1.93) 
in the solution. 
A second series of experiments gave results similar to those discussed 
above. WTien pectin alone was used as the source of carbon maceration 
in the solution and by means of the mycelium was completed in two and 
three hours, respectively. On the other hand, when glucose alone or in 
combination with pectin was employed 22 hours were required for the 
complete loss of coherence of the cells in the solution and in a water sus¬ 
pension of the mycelium. It is interesting to note in this connection 
that maceration was completed in the steamed controls in 22 hours, which 
may have been due to the acid (Ph 185 in 20 per cent dextrose and Ph 
1.70 in 20 per cent dextrose + i per cent pectin) formed. 
The results of the experiments as detailed above seem to indicate 
clearly a rather marked quantitative if not qualitative regulation of 
