Nov. 12, 1921 Pectinase Produced by Different Species of Rhizopus 377 



species produced pectinase. The amount of pectinase in the myceHum at 

 the end of the growth period was relatively small, but microsporus and 

 to a lesser degree, chinensis, exuded enough into the culture solution to 

 cause maceration in a much shorter time than either nigricans or arto- 

 carpi, both of which are parasites. Maceration of sweet-potato disks 

 by means of the mycelial enzym of the two parasitic and nonparasitic 

 species just mentioned was completed in about the same length of time. 

 Nigricans is the most commonly isolated species and is probably respon- 

 sible for most of the loss to sweet potatoes caused by this group of fungi. 

 At a suitable temperature it decays sweet potatoes and other vegetables 

 rapidly. The middle lamellae of sweet potatoes decayed by this species 

 are dissolved some distance in advance of the growth of the mycelium, 

 so that coherence is lost. In the early stages, at least, the cells them- 

 selves are not invaded by the fungus. The same may be said of artocarpi. 

 However, in cultures nigricans and artocarpi, in contrast to the other 

 species, exude a very small amount of enzym into the substrate and 

 retain very little in the mycelium. Delemar, a species which readily 

 decays sweet potatoes, seems to give up most of its pectinase to the 

 substrate, so that maceration by means of the mycelium is relatively 

 slow, at least within the limits of these experiments. All the other 

 species are vigorous parasites, decaying the sweet potato within a few 

 days under favorable conditions. They also produced large quantities 

 of pectinase, relatively speaking, some of which is exuded into the solu- 

 tion and some retained by the mycelium, as shown by the fact that 

 maceration, by both the mycelium and solution, is comparatively rapid. 



SUMMARY 



(i) The secretion of pectinase by 11 species of Rhizopus has been 

 studied. All the species were found to produce pectinase and to exude 

 some of it into the culture solution. 



(2) The amount of pectinase produced varies with the species, grown 

 under identical conditions. The mycelium of four species — nigricans, 

 microsporus, chinensis, and artocarpi — and the solution on which two — 

 nigricans, and artiocarpi — are grown is comparatively weak in pectinase. 

 Chinensis and microsporus, whose mycelial enzym is weak, secrete it 

 abundantly into the substrate. 



(3) Two species, nigricans and artocarpi, both of which are parasitic 

 on the sweet potato, secrete a relatively small amount of pectinase. 

 On the other hand, chinensis and microsporus, two nonparasitic species, 

 while retaining a small amount of enzym in the mycelium, secrete a 

 comparatively large quantity of enzym into the culture solution. 



