90 



MOLDS BELONGING TO THE PHYCOMYCETES 



rapidly to overgrow Petri plate cultures (it can cover the entire sur- 

 face of the agar in 24 hours). 



It is especially important as a cause of spoilage of fruits and 

 stored potatoes, especially sweet potatoes. The small fruits, espe- 

 cially strawberries, are particularly susceptible. The disease in 

 strawberries is known as leak, because of the softening and dripping 

 of the fruit. It is a source of considerable loss in shipment and is 

 prevented by refrigeration. In sweet potatoes, a characteristic soft 

 rot is produced, the main factors determining which are injury to 

 the potatoes and humidity of the storage bins. For a bibliography 

 of the rots caused by R. nigricans, see Heald.* 



Absidia. The genus Absidia is characterized by the formation of 

 sporangiophores arising from the arched stolons themselves (rather 



Fig. 40. Absidia sp. from soil: zj^gospore and suspensors with appendages; 

 above, diagram of sporangia and rhizoids. 



than at the holdfasts, as in Rhizopus). Further differential charac- 

 ters are the rounded or pear-shaped columella, which is quite differ- 

 ent from the flattened hemispherical columella of Rhizopus, and the 

 formation of peculiar curled filaments which surround the zygo- 

 spores, arising from the suspensors. Some species are homothallic. 

 Zygorrhynchus. In Zygorrhynchus the zygospores are formed by 

 the fusion of neighboring branches of the same hypha. This mold is 



