1 



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



it uniform in all the flasks for all organisms. Four flasks (2 liters), 

 containing 300 cc. of the culture medium, were inoculated with each 

 one of the species in each experiment, and the cultures were incubated 

 for three days. 



The macerating action was determined for the following species of 

 Rhizopus: chmensis Saito, nodosus Namysl, tritici Saito, maydis Bru- 

 derl, delemar (Boid) Wehmer and Hanzawa, arrhizus Fischer, oryzae 

 Went and Pr. Geerligs, nigricans Ehmb., reflexus Bainier, artocarpi 

 Racib., and microsporus v. Tieg. 



It has been shown ^ that the different species of Rhizopus do not all 

 have the same optimum temperture for growth. Some species thrive 

 at high temperatures, some at relatively low temperatures, and others 

 at a temperature intermediate between the two extremes. Therefore, 

 the 1 1 species studied have been separated into three groups with respect 

 to their temperature relations. In all the experiments connected with 

 the present investigations the same grouping of the different species 

 has been observed, thus subjecting each organism to as nearly the 

 optimum temperature for its growth as possible. 



The cultures of chinensis were incubated at 40° C, those of nodosus, 

 tritici, maydis, delemar, arrhizus, and oryzae at 30°, and those of nigri- 

 cans, reflexus, artocarpi, and microsporus at 20°. Although so far as 

 temperature is concerned the results are not strictly comparable, pre- 

 liminary experiments showed that more reliable data could be obtained 

 by growing the different organisms at temperatures suited to their growth 

 than by subjecting them all to a uniform temperature. Some of the 

 species, as for example nigricans, which requires a relatively low tem- 

 perature, make no growth or only a feeble growth at 30° and none at 35°. 

 On the other hand, chinensis, a high temperature form, makes a reduced 

 growth at 30° and a feeble growth at 20°. | 



At the close of the incubation period (three days) the mycelial growth 

 was lifted from the culture flask and the substrate was filtered through a 

 fine grade of muslin. The mycelium was treated subsequently by 

 acetone and ether according to the method previously described.^ The 

 solutions from the different flasks in which the same species had grown 

 were made into a compound sample thoroughly shaken, and 25-cc. 

 portions were used for maceration experiments. Likewise all the fun- 

 gous felts of the same organism grown in the different flasks were brought 

 together and treated as one sample, a weighed portion of the dried 

 mycelium being used for maceration of the raw disks. Two types of 

 controls were run with each set of experiments, as follows: (i) Sweet- 

 potato decoction on which the fungus had grown for three days, which 

 after the removal of the mycelium was steamed for 15 minutes to inac- 

 tivate the enzym; (2) decoction which was identical with that used for 



1 Harter, X,. h; Weimer, J. L., and Lauritzen, J. I. op. cit. 



2 Harter, I^. 1,., and Weimer, J. 1,. op cix 



