968 
Journal of Agricultural Research voi. xxx, No. 10 
racemosus was grown on sweet potato, 
carrot, and turnip decoctions, but not 
when grown on potato decoction. 
Only sweet potato tissue was used for 
macerating experiments, and it was 
found that it was not macerated when 
suspended in a solution of potato 
decoction in which Mucor racemosus had 
grown. It was suspected that the 
enzyme might be specific in that the 
potato would be decayed if the or¬ 
ganism was first grown on potato 
decoction. 
Sound sweet potatoes, potatoes, 
carrots, and turnips were inoculated by 
the well method from a four-days’ 
old growth of Mucor racemosus on 
sweet potato and potato decoction. 
After inoculation the hosts were kept 
at a constant temperature of 5° C. for 
32 days, then removed from the in¬ 
cubator and examined. All of the 
sweet potatoes were partially decayed 
and isolations gave pure cultures of 
M. racemosus. None of the carrots, 
turnips, or potatoes were decayed, 
which shows that M. racemosus is not 
parasitic on them, at least within the 
limits of these experiments. Whether 
or not potato decoction was used made 
no difference. 
It has already been shown that Mucor 
racemosus when grown on turnip and 
carrot decoction secretes into the solu¬ 
tion a substance which will macerate 
raw sweet potato tissue, although the 
fungus is not parasitic on either carrot 
or turnip. In view of this fact an ex¬ 
periment was outlined for the purpose 
of determining if when grown on sweet 
potato decoction a substance is produced 
which will macerate raw turnip and 
carrot disks. These experiments were 
carried out in the usual way by the use 
of 2-liter Erlenmeyer flasks, which after 
inoculation were incubated at 10° C. 
After 14 days of growth the solutions 
were freed of mycelium by filtering 
through absorbent cotton. Disks of raw 
sweet potato, carrot, and turnip 1 mm. 
thick were suspended in the solutions 
and incubated at 35°. The results 
showed that maceration was started in 
every case in about 3J^ hours and was 
nearly complete in 5 hours. It is 
evident from these investigations that 
M. racemosus will secrete into the 
substrate a substance which will dis¬ 
solve the middle lamellae of hosts of 
which it is not a parasite. 
SUMMARY 
The secretion of pectinase by Mucor 
racemosus which causes a rot of sweet 
potatoes at a temperature of 5° C. and 
lower, and by Diplodia tubericola, the 
cause of a slow dry-rot at higher 
temperatures, was tried on 10 different 
culture media. D. tubericola did not 
secrete the enzyme. M. racemosus 
produced it on certain vegetable 
decoctions (sweet potato, carrot, tur¬ 
nip, string bean), but not on prune or 
potato decoction, or on synthetic 
media (Czapek’s, Richard’s, Pfeffer’s) 
and beef bouillon. 
Both Mucor racemosus and Diplodia 
tubericola secreted the enzymes, 
amylase, invertase, and raffinase, but 
not cytase. 
The influence of these two fungi on 
the hvdrogen-ion concentration of the 
10 substrates used was investigated 
with the following results: M. racemosus 
decreased the hydrogen-ion concentra¬ 
tion of sweet-potato, carrot, potato, 
turnip, and string-bean decoction, and 
of beef bouillon, and increased that of 
prune decoction and of Czapek’s 
modified nutrient solution. There was 
no appreciable change of Pfeffer’s and 
Richard’s solutions. D. tubericola de¬ 
creased the hvdrogen-ion concentra¬ 
tion of all of the vegetable decoctions 
(prune, slightly) and of beef bouillon. 
The hvdrogen-ion concentration was 
increased when grown on Czapek’s, 
Pfeffer’s, and Richard’s solutions. 
Mucor racemosus was found to be 
parasitic on sweet potatoes, but not on 
turnips, carrots, or potatoes. The 
growth of this organism on potatoes 
did not produce an enzyme which 
would macerate potato tissue. Al¬ 
though not parasitic on turnips and 
carrots, an enzyme which would 
macerate sweet-potato disks was 
produced when grown on decoctions 
made from these vegetables. When 
the organism was grown on sweet- 
potato decoction an enzyme which 
would macerate turnip and carrot 
tissue was secreted. 
LITERATURE CITED 
(1) Clark, W. B. 
1918. VOLUMETRIC DETERMINATION OF REDUCING 
SUGARS. A SIMPLIFICATION OF SCALES’ METHOD 
FOR TITRATING THE REDUCED COPPER WITHOUT 
REMOVING IT FROM THE RESIDUAL COPPER SOLU¬ 
TION. Jour. Amer. Chem. Soc. 40: 1759-1772, 
illus. 
(2) Dox, A. W. 
1910. THE INTRACELLULAR ENZYMS OF PENICIL- 
LIUM AND ASPERGILLUS, WITH SPECIAL REFER¬ 
ENCE TO THOSE OF PENICILLIUM CAMFMBERTI. 
U. S. Dept. Agr., Bur. Anim. Indus. Bui. 
120, 70 p. 
(3) Harter, L. L., Weimer, J. L., and Adams, 
J. M. R. 
1918. sweet-potato storage rots. Jour. Agr. 
Research 15: 337-368, illus. 
(4) -and Weimer, J. L. 
1921. a comparison of the pectinase produced 
by different species of RHizopus. Jour. Agr. 
Research 22: 371-377, illus. 
