34 BULLETIN 727, U. S. DEPARTMENT OF AGRICULTURE. 



during the early part of July and a heavy rain on July 22, followed 

 by temperatures favorable to this fungus, should have induced an 

 early development of anthracnose. Although there were frequent 

 rains during the remainder of the season, all daily mean temperatures 

 remained well below 75° F., the optimum for the anthracnose fungus. 

 The mean monthly temperature for August was 67° F., and for the 

 first week of September, 63° F. 



Anthracnose was first found on July 27 in field 1 and consisted at 

 that time of eight infected plants scattered through four rows. On 

 August 1 there was considerable anthracnose in 12 rows in the north- 

 west corner of the field, in 3 rows in the southeast corner, and in a 

 detached block at the southwest corner. This infection did not 

 appear in typical original centers, but rather as scattered and com- 

 paratively recently infected plants. On August 13 anthracnose was 

 found in a total of 28 rows scattered through the field, but was in no 

 case serious. Inspections made August 25 and September 8 showed 

 that no extensive spread had occurred. This can not be attributed 

 to lack of rain and is probably due to the low daily mean tempera- 

 tures prevailing after the end of July, as noted above. 



In the other fields no anthracnose was found except in the Isom 

 field, and there not until August 13, when old lesions were noted on. 

 the old leaves of two adjacent plants. On September 8 an additional 

 original center from which very little spread had occurred was found. 

 Why these were so late in developing is not understood. 



LOCAL DISSEMINATION BY WATER AND OTHER AGENCIES. 



Consideration of the subject of dissemination falls very naturally 

 into two general categories: One, the mode of spread of the disease 

 in the field during the growing season; the other, the manner in 

 which the disease is first introduced into new fields (21). The former 

 may conveniently be considered as local dissemination. 



SPATTERING ACTION OF RAIN. 



That water is essential to the separation and dispersal of the spores 

 of this type of fungus is generally recognized. Since the spores tend 

 to remain in masses adherent to the acervuli until their matrix is 

 dissolved by water, the importance of the latter as a prerequisite for 

 spore dispersal is quite evident. But the mechanical action of rain 

 is more important. 



The appearance of so-called centers in fields has been mentioned. 

 The gradual enlargement of these foci of infection and the spread 

 therefrom is the phase with which we are now concerned. Some of 

 the experimental work on water dissemination has been previously 

 reported (21). 



Observations made in the Madison fields in 1916 showed that an 

 enlargement of old centers of infection in all directions was to be 



