236 Diseases of Truck Crops 



The top end is broadest, becoming dilated into a 

 caputate vesicle. From this head are produced from 

 a few to a dozen small branches, the tips of each in 

 turn becoming vesicular (fig. 41 c). Each vesicle 

 now becomes covered with a dense layer of conidia 

 (fig. 41 d). The latter are light to reddish brown 

 in color (fig. 41 e). The conidia germinate by means 

 of a germ tube. Sporangia are formed in pure 

 culture but not on the host. Sporangia are first 

 evident as white pendant enlargements, becoming 

 separated from the sporangiophore by a globular 

 columella (fig. 41 f). Mature sporangiospores are 

 larger than the conidia, are smooth, and possess 

 terminal hyaline appendages (fig. 41 g). The spores 

 germinate by means of the germ tube, as is the case 

 with the conidia. Chlamydospores are not uncom- 

 mon and they have often been observed during the 

 winter. The formation of zygospores is a common 

 occurrence on culture media, but not on the host. 

 The method of zygospore formation and germina- 

 tion has not as yet been definitely worked out. 



Control. The spores of Choanophora cucurbitarum 

 are undoubtedly carried from flower to flower by 

 insects. Spraying, as outlined for cucumbers, is also 

 recommended for the squash, p. 232. 



SOFT ROT 

 Caused by Rhizopus nigricans Ehr. 



Soft rot very often cannot be distinguished from 

 the fruit rot above mentioned (fig. 41 j). The symp- 



