44 BULLETIN 727/ U. S. DEPARTMENT OF AGRICULTURE. 



large field near Quitman, Ga., considerable new infection in the shape of 

 rather isolated infected leaves or groups of leaves was found out along 

 the rows just outside of extensive heavily infected areas. These new 

 infections were not downhill from the old centers nor was infection 

 continuous along the row, so water dissemination was precluded. As 

 a rule, these infections consisted of only a few older lesions, not scat- 

 tered over the whole leaf blade, but commonly along one edge or along 

 a vein. From these older lesions some secondary infection had oc- 

 curred. The most striking feature of these incipient centers of infec- 

 tion was, however, that about two out of three were located on the 

 leaves immediately surrounding or overhanging a fruit. About the 

 edge of one area of old infection, 68 of these scattered new infections 

 were found on foliage around fruits. This represented probably 5 

 to 10 per cent of all fruits lying within the area examined. 



Upon inquiry of the plantation manager, it was learned that 

 about two weeks previously the field had been gone over for the pur- 

 pose of removing the malformed and rotting fruits. This period of 

 time coincided well with the apparent age of the older leaf lesions 

 above noted. This " culling" operation, it appears, is usually per- 

 formed early in the morning when the vines are wet with dew. At any 

 rate, in the case under consideration, all the evidence pointed to hand 

 dissemination during the process of culling the vines. A likely hypothe- 

 sis is that, in going up one row and down the next, the workman had 

 repeatedly passed through the badly diseased area, had removed dis- 

 eased fruits, and carrying spores on his hands had unconsciously in- 

 oculated the foliage farther along as he pushed the leaves aside to gain 

 an unobstructed view of a fruit or to see if a f mit was concealed under 

 the heavy f oliage. 



From these leaf lesions, spores are readily washed to the fruit un- 

 derneath, and the insidiousness of these "hand'' infections becomes 

 obvious when it is realized that the new centers are so located that 

 the worst possible damage is an immediate result. 



The chief activity of man in local dissemination is, then, in inocu- 

 lating leaves here and there along the row, which act as new centers 

 of infection. Among watermelons, rather conclusive evidence of this 

 type of disease dispersal has been obtained. 



DISSEMINATION WITH THE SEED. 



It is in the introduction of the disease into new fields that human 

 agencies assume prime importance. Here will be considered some 

 of the possible sources of infection. The overwintering of the fungus 

 in the field is treated in a later chapter. The disease has not been 

 found on wild cucurbits in the North. The occurrence of Lagenaria 

 gourds and volunteer melon vines in the South is recognized as a pos- 

 sible source of infection. Country- wide transport of diseased water- 



