6 BULLETIN 531, U. S. DEPARTMENT OF AGRICULTURE. 
the diameter of hyphae do. not seem to vary greatly with the different 
humidities. The hyphse range from 10 to 40 \l in thickness, mostly 
20 to 30 \x. The spores are variable in shape and size, being round to 
oval, or even very irregular, 5 to 15 p. in diameter, the large irregular 
spores often reaching a length of 27 to 28 pi. 
The extreme length of the sporangiophore is apparently developed 
only in saturated or nearly saturated air. "When the fungus fruits 
on berries in the field or on the tops of boxes exposed to the open air 
the sporangiophores are short. Near the bottoms of boxes or in 
closed containers in which the juice leaking from the berries raises 
the moisture content of the air to near saturation, long sporangio- 
phores are developed. So great is this difference that it might readily 
be assumed that two species of Rhizopus rather than one were con- 
cerned. The fact that rhizoids ordinarily are produced below the 
epidermis of the strawberry in dry air, whereas they are often borne 
above the surface in moist air, adds to the difference in the appear- 
ance of the two forms. 
A fact which might readily mislead an investigator as to the true 
cause of rot in strawberries is the extreme susceptibility of Rhizopus 
to alcohol vapor. During the early part of the writers' investiga- 
tions it was customary to place decayed berries in moist chambers. 
The juice leaking from the berries soon raised the humidity to sat- 
uration. Yeast developed on this liquid, and alcohol was produced 
so abundantly that its odor was distinctly noticeable. Under these 
conditions many rotten berries produced no fruiting bodies of any 
fungus. 
Finally it was observed that if the covers of the moist chambers 
were removed and the liquid taken up with blotting paper, mature 
sporangia of Rhizopus nigricans would develop on a large number 
of the rotten berries overnight. This led to an investigation of the 
effect of alcohol «fumes on the fruiting of this fungus. 
In this investigation Hempel desiccators containing alcohol of 
various strengths were used (200 c. c. of alcohol solution per desic- 
cator). It was found that berries inoculated with Rhizopus would 
rot under 95 per cent alcohol without producing any fruiting bodies. 
The same thing proved true of all strengths of alcohol down to 2 per 
cent. With 2 per cent alcohol aerial mycelium developed, but no 
sporangia were produced; with 1J per cent alcohol apparently normal 
sporangia on short sporangiophores developed. 
In 1896 Goff (6) found that strawberries exposed to alcohol vapor 
under a bell jar in a refrigerator did not mold, while similar berries 
kept in the same refrigerator but not exposed to alcohol vapor 
molded considerably; he makes no mention, however, of the species 
of fungi present. 
