6 BULLETIN 531, IT. S. DEPARTMENT OF AGRICULTURE. 



the diameter of hyphse do not seem to vary greatly with the different 

 humidities. The hyphse range from 10 to 40 [/, 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 \i. in diameter, the large irregular 

 spores often reaching a length of 27 to 28 \k. 



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 Rfiizopus 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 1£ per cent alcohol apparently normal 

 sporangia on short sporangiophores developed. 



In 189G 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. 



