254 AMERICAN JOURNAL OF BOTANY [Vol. io, 
potatoes, after being cut in halves and dipped in a spore suspension, were 
confined in deep preserving jars. Some of the jars were plugged with 
cotton, some were left open, and others were closed with a close-fitting 
glass stopper. No decay took place, either in the jars that were left open 
or in those that were closed by glass stoppers. In the former case, some 
hyphae grew on some of the potatoes but no infection resulted. In the 
latter case, no hyphae were seen, which was probably due to the fact that 
the carbon dioxid which accumulated in the jar was injurious to the fungus. 
Saturated filter paper or cotton in the bottom of the jars did not materially 
increase the percentage of decay. If, however, air is constantly pulled 
through water and then through the jar, infection takes place. On the 
other hand, air circulation was unnecessary when the germinated spores 
and decoction on which they grew were poured into the “well,” since it 
was found that, if the cover glass over the well was sealed on airtight, 
infection would still take place. 
The Part Played by Enzyms 
In this connection the writers have in mind pectinase, which they have 
shown is abundantly produced by Rhizopus, and which they have found is 
capable of macerating the tissue of sweet potatoes (18). It has been 
demonstrated that a part of this enzym is exuded from the mycelium into 
the substrate; also that a watery extract of the mycelium and the enzym 
exuded into the solution on which the fungus had grown would disintegrate 
the tissue of thin sweet-potato disks in from 2 to 4 hours. It is likely that 
pectinase passes into the substrate almost immediately upon the germination 
of the spores, and it is not unlikely that it may diffuse from the spores 
even before germination, since it has been shown that a watery extract of 
the spores will macerate raw sweet-potato tissue 1 in the same identical way 
as an extract of the hyphae or as the solution on which the fungus has 
grown. Although the exudation of pectinase into the substrate from living 
ungerminated spores has not been demonstrated, it has been shown that it 
is exuded into the solution soon after germination. The following experi¬ 
ment was designed especially to throw some light upon this question. 
A large volume of spores of R . tritici was suspended in sweet-potato decoc¬ 
tion in 2-liter Erlenmeyer flasks and incubated at 35 0 C. After 6 hours, 
the decoction from one of the flasks was filtered through no. 2 Whatman 
filter paper to remove the spores and mycelium. Raw sweet-potato disks 
R2 mm. thick and 1.5 cm. in diameter were partially macerated in the 
solution in 24 hours. A control of the same solution steamed to inactivate 
the enzym produced no maceration. Only a part of the spores were germi¬ 
nated, with germ tubes varying from one to several times the diameter of 
the spore. At this stage it is to be expected that there would be only a 
minimum amount of pectinase present. The strength of the macerating 
1 Results not yet prepared for publication. 
