540 Journal of Agricultural Research voi.xvni, no. io 



mold per cubic centimeter at the highest concentration employed (which 

 was at the saturation point) there was a gain of 2.41 per cent in reducing 

 sugars over the control, while with double the number of spores of 

 PenicUlium expansum there was only one-fourth that gain in reducing 

 sugars. Five times as many spores of Aspergillus niger produced one- 

 fourth greater increase in reducing sugars. 



In general, then, it will be seen that the invertase activity of these mold 

 spores is directly influenced by concentration in the manner described, 

 and furthermore that it is likewise dependent on the number of spores 

 employed. The second part of this paper, therefore, is concerned with 

 the influence of numbers of mold spores upon their invertase activity in 

 sugar solutions at the saturation point. 



Since there has been occasion in another connection ' to study the in- 

 fluence of the number of mold spores, somewhat the same procedure was 

 employed in this experiment. The spore suspensions were prepared as 

 described in an earlier paper,^ and the proper dilutions made with sterile 

 distilled water. The same conditions of incubation, etc., were again 

 observed. The control flasks contained a mixture of spores of all dilu- 

 tions heated to 100° C. for }4 hour. The largest number of spores of 

 PenicUlium expansum and Aspergillus niger was about 400,000 per cubic 

 centimeter, and the largest number of blue aspergillus was about 80,000. 

 The dilutions represented an arithmetic progression of one-half of the 

 preceding quantity. 



In Table IV will be found results obtained with varying quantities of 

 inoculum in a sugar solution at the point of saturation. 



Some striking differences are to be noted where the blue aspergillus 

 was used. With a decrease in quantity of inoculum there is a proportional 

 decrease in invertase activity until 5,000 spores are employed, at which 

 point no significant inversion occurs. Consequently that number may 

 be taken as the lowest limit essential to invertase activity in such a highly 

 concentrated sugar solution. 



On the other hand, PenicUlium expansutn is not nearly so effective, for 

 it will be seen that while there is a decrease in invertase activity with a 

 decrease in number of spores, nevertheless the minimum is reached 

 between 110,000 and 55,000 per cubic centimeter, which is practically 

 10 times as great an amount as was required by the blue aspergillus. The 

 lower limits of the invertase activity of PenicUlium expansum, however, 

 are very sharply defined. The results obtained with Aspergillus niger are 

 practically identical qualitatively with those observed for PenicUlium 

 expansum, but vary in the quantitative relationships. To a certain degree 

 this is probably accounted for by the fact that the latter mold had the 

 larger inoculation. 



1 KoPELOFF, Nicholas, inoculation and incubation of soil fungi. In Soil Sci., v. i, no. 4, p. 

 381-403. 1916. Literature cited, p. 402-403. 

 2 and KoPELOFF, Lillian, do mold spores contain enzyms ? In Jour. Agr. Research, v. 18, 



no. 4, p. 195-209. 1919. 



