876 
Journal of Agricultural Research 
Vol. XXIV, No. 10 
which the retarding action of the mineral acids increased much more 
rapidly. A concentration was finally reached where maceration was 
caused by the acid. Brown in his studies used dilutions of normal acids, 
so his results can not be compared directly with those of the writers, 
who studied the action of the acids in terms of hydrogen-ion concentra¬ 
tions. That the acid formed in Czapek’s solution did not inactivate 
the enzym may be inferred from the following facts. When Czapek’s 
solution, which was made acid (Ph 1.8) by the growTh of the fungus, 
was changed to a Ph of 7.8 and raw sweet-potato disks added no macera¬ 
tion took place. It had been previously shown that the enzym was 
not inactivated at Ph of 10. The solution was not alkaline enough to 
inactivate the enzym. Some of the data obtained with sweet-potato 
decoction may be cited as further evidence. It has been shown (Table 
V) that maceration in sweet-potato decoction is complete in 2^ hours at 
a Ph of 2.55. On the other hand, in Czapek’s solution with a Ph of 2.66 
(Table III) which is even less acid no maceration occurred in 48 hours. 
Although there is a difference in the composition of these two media, it 
is reasonable to assume that since the acid was not sufficiently strong in 
the sweet-potato decoction (Ph 2.55) to inhibit the action of the enzym 
it would not be able to do so in the less acid Czapek’s solution (Ph 2.66). 
The investigations of the authors showed that the presence of pectinase 
in the mycelium grown on Czapek's nutrient solution could not be dem¬ 
onstrated, while it occurred regularly in the hyphae produced on sweet- 
potato decoction. If the enzym was produced, its occurrence in the 
hyphae on Czapek’s solution as well as on sweet-potato decoction would 
be expected. Furthermore, the enzym in the mycelium, if it occurred 
there, would not be inactivated by the acid in the substrate, since the 
mycelium is always suspended dn distilled water, which is practically 
neutral. 
SUMMARY 
(1) Rhizopus tritici, a fungus capable of causing the softrot of sweet 
potatoes was used in all these experiments. On suitable media it pro¬ 
duces a powerful enzym, called pectinase, which dissolved the middle 
lamellae of raw sweet-potato and carrot disks. 
(2) A comparison of the production of the enzym was made on the 
following media: String bean, prune, Irish potato, carrot, turnip, and 
sweet-potato decoction, and on Czapek’s, Peffer’s, and Richard’s syn¬ 
thetic media and on beef bouillon. 
(3) It was found that the cell wall dissolving enzym was produced 
on all the vegetable media except prune decoction, but not on the syn¬ 
thetic media with glucose as a source of carbon or on beef bouillon. 
(4) If pectin was used alone as a source of carbon in Czapek’s nutrient 
solution, an active enzym was produced. When pectin was combined 
with glucose the action on raw sweet-potato disks was feeble. 
(5) When Rhizopus tritici was grown in Czapek’s nutrient solution 
with glucose as a source of carbon the substrate became sufficiently acid 
to cause dissolution of the middle lamellae so that coherence of the cells 
was completely lost in from 6 to 24 hours. 
(6) The production of the macerating principle by the fungus when 
growing on Czapek’s nutrient solution and sweet-potato decoction was 
not influenced by adjusting these solutions to different Ph values. The 
enzym was not produced in Czapek’s solution at any hydrogen-ion 
