Nov. 12, 1921 Pectinase Produced by Different Species of Rhizopus 375 



DISCUSSION OF RESULTS 

 VARIATION 



A comparison of the results as shown by figures i and 2 indicates that 

 under the conditions of these experiments maceration was completed by 

 the enzym exuded into the solution in a shorter length of time than by 

 that contained in the mycelium. This difference, however, does not 

 mean that the enzym is more powerful or more abundant in the solution 

 than in the mycelium since no attempt was made to employ an amount of 

 mycelium that would be equivalent in macerating power to the enzym 

 of the solution. In these experiments maceration was regarded as 

 complete when the disks pulled from opposite sides separated without 

 any perceptible resistance. In completely macerated tissue coherence 

 of the cells is entirely lost and the tissue can be readily pulped between 

 the thumb and finger. 



The data show that a considerable amount of variation exists in the 

 results obtained in the different experiments with a single species both in 

 respect to the solution and the mycelium. There are probably several 

 factors responsible for these variations. In the first place a dififerent 

 supply of the sweet-potato decoction was prepared for each set of experi- 

 ments. In spite of the fact that the dififerent solutions were prepared 

 to be alike as nearly as it is possible to make them, it can not be said, in 

 view of the fact that different potatoes were used each time, that the 

 various preparations were identical. After the cultures were inoculated 

 incubation was carried out at a temperature which varied very little 

 but possibly enough to influence slightly the rapidity and volume of 

 growth. At the close of the incubation period the substrate and mycel- 

 ium were handled as nearly alike as possible in all the experiments, but 

 in spite of such precautions some variations might result. It would seem 

 that the greatest source of error might be attributed to a variation in the 

 composition of the potatoes from which the raw disks were cut. In this 

 connection preliminary experiments showed that different potatoes are 

 macerated in a dififerent length of time the variations, however, being 

 within relatively narrow limits. Furthermore, it is probable that the 

 composition of the sweet potato is gradually changing with the increase 

 in the length of time after digging. So far as their susceptibility to 

 maceration is concerned it is interesting to note that a comparison 

 between newly dug potatoes and those stored for several months showed 

 that the latter are macerated in a shorter time than the former. Although 

 the present experiments were carried out with a single variety the various 

 experiments were conducted in sequence so that the later experiments 

 were made on what might be termed older potatoes. 



