Apr., 1923] WEIMER AND HARTER-PECTINASE IN RHIZOPUS 
I69 
was held in which the spore suspension was heated in order to inactivate the 
enzym. Maceration was carried out at a temperature of 35 0 C. A little 
toluol was added to each flask to prevent the growth of contaminating 
bacteria. 
The enzym was relatively dilute, so that maceration progressed rather 
slowly. No maceration occurred in the control flasks. In the other flasks 
the discs became somewhat crisp at first but later became flaccid. This 
stage was then followed by a dissolution of the middle lamellae, which was 
typical in every respect of that produced by a water extract of the mycelium 
or by the> solution on which the fungus grew. 
The rate of the maceration by the enzym produced by the spores of these 
two species differed considerably. The action by R. tritici was relatively 
rapid, the discs being completely macerated in 24 to 48 hours. Rhizopus 
nigricans , on the other hand, acted very slowly, and in some cases no 
maceration took place in 72 hours. The writers have found also that the 
enzym per unit volume of solution or per unit weight of mycelium is much 
weaker in R. nigricans than in R. tritici. Without going further into the 
details of these experiments or their results, the evidence conclusively shows 
that the spores of both species contain an enzym which is able to cause 
disintegration of the middle lamellae of raw sweet potatoes. 
It is very likely that this enzym plays an important role in the early 
nutrition of the fungus and that it may be a factor in the initial infection 
of some of its hosts. 
Summary 
The spores of Rhizopus nigricans and R. tritici both contain an enzym, 
pectinase, which is capable of dissolving the middle lamellae of raw sweet 
potatoes. The rate of maceration by the spores of R. nigricans is relatively 
much slower than that produced by the spores of R. tritici when the con¬ 
centration of the spores by weight is the same. 
U. S. Department of Agriculture, 
Washington, D. C. 
