204 Journal of Agricultural Research voi. xiii, N0.3 



show signs of disintegration — that is, they lose chromatin and become 

 more or less fragmented. The vascular portions of the leaf are not 

 involved until such time as the toxic substances resulting from growth 

 of the fungus have brought about disorganization of all the other tissue 

 systems. When this occurs, a mass of disintegrated cells is seen inter- 

 spersed with a few cells still retaining their original contour, but whose 

 protoplasmic contents have been changed to dark-colored, more or 

 less opaque coagulation products. In early stages the diseased cells 

 may contain one to several brown, oily-appearing droplets, surrounded 

 by either a few of the still intact chloroplasts and a fragmented nucleus, 

 or dense coagulation products. 



MODE OF ENTRANCE 



From the experiments here reported it is apparent that the fungus is 

 a wound parasite. As already noted in one experiment infection fol- 

 lowed inoculation by spraying on a suspension of the spores in water, 

 no needle-pricks being made. However, it was not possible in this 

 case to demonstrate by microscopic sections that the hyphae had entered 

 through the stomata, although a good many sections, both vertical 

 and horizontal, were carefully examined. Slight wounds are almost 

 always present, through which the hyphae might easily enter. 



CULTURAL STUDIES 

 CULTURAL CHARACTERS 



It was found that the fungus grows most rapidly, and produces the 

 greatest abundance of pycnidia on steamed com meal in flasks, and on 

 steamed potato cylinders standing in test tubes in about i c. c. of distilled 

 water. Transfers were made from these media to corn-meal agar; 

 steamed string beans; beef agar; synthetic agar,^ Kalmia agar; steamed 

 leaves and twigs of K. latifolia; steamed com meal plus litmus milk; 

 litmus milk; litmus agar plus various sugars (saccharose, maltose, 

 lactose, dextrose, galactose, mannit); plain litmus agar; com-meal 

 agar plus saccharose, maltose, and dextrose; Uschinsky's solution; 

 Cohn's solution; Dunham's solution; peptonized beef bouillon; beef 

 gelatin; milk; sterile distilled water; potato juice in fermentation 

 tubes. On a majority of these media few or no pycnidia are formed. 

 On steamed com meal the spores germinate in 24 to 48 hours, forming 

 a pure -white, delicate mycelium which soon covers the surface of the 



1 Prepared according to the formula furnished this laboratory by Mr. Frederick V. Rand: (a) i, 500 c. c. 

 of distilled 'water and 36 gm. of agar. Cook in double boiler for one hour at 15 pounds, pressure. (6) 

 500 c. c. of distilled water, 200 gm. of dextrose, 40 gm. of peptone, 20 gm. of ammonium nitrate, 5 gm. of 

 magnesium sulphate (crystals), 10 gm. of potassium nitrate, 5 gm. of potassium acid phosphate, and 0.2 gm. 

 of sodittm chlorid. Boil in a double boiler for 30 minutes, add agar, and cook for s minutes. Restore 

 volume, titrate, cool to 60° C, and add whites of two eggs. Cook to coagulate eggs, filter, tube, and ster- 

 ilize. This formula is modified from that given by Darwin and Hamilton. (Darwin, Francis, and 

 Acton, E. H., practicai, physiology of plants, ed. 3, p. 68. Cambridge, 1901.) 



