376 Journal of Agricultural Research voi. xxii. no. 7 



COMPARISON OF SPECIES 

 MACERATION OP DISKS IN THE SOLUTIONS 



It appears from figure i that two species, nigricans and artocarpi, 

 macerate raw sweet potato disks more slowly than any of the others, 

 followed by chinensis and reflcxus in the order mentioned. The other 

 species complete maceration in a relatively short time, the most rapid 

 being arrhizus, tritici, and maydis. 



MACERATION OF DISKS IN A SUSPENSION OF MYCELIUM 



With respect to maceration by the mycelial enzym, four species, 

 nigricans, micros porus, chinensis, and artocarpi, stand out as being conspic- 

 uously slow. So far as the mycelium is concerned delemar, a species inter- 

 mediate between the slow and rapid forms, is less active than reflexus but 

 more active than the latter when the solutions are used. Likewise the 

 enzym contained in the mycelium of micros porus macerates slowly, while 

 that in the solution, on the other hand, disintegrates the tissue rapidly. 

 Chinensis shows a similar relationship existing between the enzym of the 

 mycelium and that of the solution, although this species does not stand 

 out as conspicuously as microsporus. 



From the few illustrations cited it is evident that there is no complete 

 correlation between the activity of the mycelial enzym and the activity 

 of that exuded into the substrate. An examination of figures i and 2 

 shows that the different species do not secrete an equivalent amount of 

 pectinase, since the completion of maceration by the enzym of both the 

 mycelium and solution may vary greatly. It is conceivable and the 

 results of these investigations seem to indicate that some species give up 

 their enzym to the solution more readily than others. For example, the 

 solution on which tnicrosporus grew is relatively rich in pectinase while 

 the enzym contained in the mycelium acts slowly. Delemar is another 

 outstanding example of the same phenomenon. 



PECTINASE PRODUCTION IN RELATION TO PARASITISM 



If a relationship between the production of pectinase by the different 

 species of Rhizopus and their parasitism could be shown to exist, con- 

 siderable light might be thrown on the physiology of parasitism, espe- 

 cially among fungi which are characterized by their ability to dissolve 

 the middle lamella in advance of their growth. In a previous publica- 

 tion ^ it was pointed out that all the species of Rhizopus studied were 

 parasitic on sweet potatoes with the exception of microsporus and chinen- 

 sis. These two species were studied in connection with the others. 

 They were given equal opportunity to cause decay, but in no case was 

 there any evidence to indicate parasitism. However, both of these 



iHarter, L. L., Weimbr, J. L., and Lauritzen, J. I. op. cix. 



