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AMERICAN JOURNAL OF BOTANY 
[Vol. io. 
a nonparasitic species, the difference is quite marked. Unfortunately, 
some of the organisms would not grow at 40° and 30° C. and others at 9 0 , 
at least within the time allowed. It is evident from table 1 that nigricans , 
the principal cause of soft-rot of sweet potatoes, produces a very small 
amount of pectinase at 9 0 . The conclusion from the results shown in table 
2 is that potatoes which have been cured and kept in storage for several 
months are more readily macerated than those freshly dug, the difference 
in most cases being very marked. The time required to macerate old 
potatoes is on an average about one half that required to dissolve the middle 
lamellae of new ones, as regards both the enzym exuded into the substrate 
and that retained by the mycelium. These results would seem to accord 
with the general observation that the susceptibility of sweet potatoes to 
decay increases with the increase in length of time they are held in storage. 
Summary 
1. The influence of temperature on pectinase production by the following 
species of Rhizopus was studied: nigricans , reflexus, microsporus, delemar, 
oryzae, chinensis, nodosus , tritici , and maydis. These experiments seem to 
indicate that the enzym is produced at any temperature at which the fungi 
will grow. Temperatures of 9 0 , 20°, 30°, and 40° C. were employed. 
2. The amount of enzym produced was least at the highest temperature, 
as regards both that exuded into the substrate and that retained in the my¬ 
celium. The quantity of enzym in the mycelium was found to increase with 
a decrease in the temperature down to and including 9 0 C. Similar results 
were obtained with the solution, except that a slight reduction resulted 
in the quantity of enzym produced when the temperature was lowered 
from 20 0 to 9 0 . 
3. The nonparasitic species ( microsporus and chinensis ) produced a con¬ 
siderable quantity of enzym, whereas nigricans , one of the parasitic species, 
produced a very small amount. 
4. A comparison was made of the relative length of time required by 
the enzym produced by the different species to macerate the tissue of 
freshly dug sweet potatoes and of those which had been held in storage for 
several months. The fungi were grown at three different temperatures: 
40°, 30°, and 9 0 C., maceration being carried out at 40°. In general, it was 
found that the middle lamellae of old potatoes were dissolved in about 
one half the time required to macerate the tissue of new ones. 
U. S. Department of Agriculture, 
Washington, D. C. 
LITERATURE CITED 
1. Harter, L. L., Weimer, J. L., and Lauritzen, J. I. The decay of sweet potatoes ( Ipomaea 
batatas ) produced by different species of Rhizopus. Phytopath. 11: 279-284. 1921. 
2. Harter, L. L., and Weimer, J. L. A comparison of the pectinase produced by different 
species of Rhizopus. Jour. Agr. Res. 22: 371-377. 1921. 
3. -Studies in the physiology of parasitism with special reference to the secretion of 
pectinase by Rhizopus tritici Saito. Jour. Agr. Res. 21: 609-625. 1921. 
4. Harter, L. L. Amylase of Rhizopus tritici, with a consideration of its secretion and action. 
Jour. Agr. Res. 20: 761-786. 1921. Literature cited, pp. 784-786. 
