Aug. i, 1921 
Studies in the Physiology of Parasitism 
617 
the middle lamellae of sweet-potato disks so that the cells fall apart 
without the cells themselves undergoing any apparent mechanical altera¬ 
tion. 
INFLUENCE) OF THE AGE OF THE MYCELIUM ON THE RATE OF MACERATION 
Brown (4, 1 ) showed that the young, growing hyphae of Botrytis cinerea 
contained a more powerful enzym than old hyphae, and he used for 
most of his work an extract of the fungus grown for only 24 hours. Other 
investigators have obtained similar results for other enzyms of various 
fungi. It appears to be generally agreed that the most powerful extract 
is obtainable from young or comparatively young hyphae, but it can not 
be expected that all fungi will show the same limitations as regards the 
length of time for growth. This being a question of considerable impor¬ 
tance with respect to much of the future investigations in this direction, 
experiments were planned and carried out in considerable detail for the 
purpose of determining at what period in the growth of the organism 
the most powerful extract could be obtained from the hyphae, and 
likewise when the maximum amount of the enzym was present in the 
solution. While it may be argued that comparative studies do not neces¬ 
sarily require that the work be done with hyphae and solutions containing 
the maximum amount of enzym, there are several reasons why it is de¬ 
sirable to do so. First, the time required to complete maceration is 
shortened so that the experiments may be completed within a single day. 
Second, a short period of maceration eliminates to a large extent the 
influence that might be exercised by the introduction of contaminating 
organisms. Third, infection is essentially dependent upon the extra¬ 
cellular enzym of young hyphae, at least in so far as enzyms play a part. 
To determine the period of maximum content of enzym in the hyphae 
and in the solutions, 50 flasks containing sweet-potato decoction and 36 
inoculated with spores of Rhizopus tritici were prepared. All the flasks 
were incubated at 3 7.5 0 C. in the dark. At the end of each 24-hour 
period, with exceptions to be noted in the following table, 4 of the flasks 
(3 inoculated and 1 not inoculated) were taken from the incubator, the 
fungous felt was removed, and the solution was filtered through absorb¬ 
ent cotton. The hyphae from the inoculated flasks were treated in the 
usual way with acetone and ether, and after drying the fungous material 
was made into one compound sample. Duplicate 0.25-gm. samples of 
the hyphae were weighed out, ground in sand, suspended in 25 cc. of 
distilled water, and used for the maceration of the sweet-potato disks. 
A water blank containing no enzym powder was used as a control. The 
incubation temperature was 37.5 0 . Records were made from time to 
time of the progress of maceration. 
The contents of one of the three flasks on which the fungus had grown 
were steamed to deactivate the enzym, and together with one flask not 
