8 Journal of Agricultural Research vol. xx, no. i 



infection is a slightly brown and water-soaked spot, 2 to 3 mm. in length, 

 on the glumes. The veins appear more water-soaked and have a much 

 darker olive-green appearance than the area between them. The points 

 at which the infected glume or glumes are attached to the rachis soon show 

 the water-soaked appearance also. The water-soaked area increases 

 more or less rapidly, depending on weather conditions, until the whole 

 spikelet is covered. It then spreads to the neighboring spikelets. 



If the weather is dry the infection may remain restricted to one spike- 

 let. At this time the glumes and the spikelets originally infected gradu- 

 ally begin to lose the water-soaked appearance, dry up, and take on the 

 typical color of the ripe head of the particular variety. This drying up 

 of the infected spikelets follows closely the advancing infection, which 

 usually proceeds downward, as was first observed by Freeman (2, p. 310) 

 in 1905. The healthy part of the head above the point of infection 

 usually dries up and dies without passing through the water-soaked stage, 

 because of the cutting off of the water and food supply by the fungus at 

 the point of infection. In some cases, however, one or more vascular 

 bundles of the rachis may remain free from the fungous invasion and con- 

 tinue to supply the uninfected portion of the head with water and food 

 until the head has ripened normally and has formed fairly normal kernels. 

 When infection proceeds down the stem, producing the same symptoms 

 as on the head, it may sometimes reach as far as the upper node. Here, 

 too, the whole or only one side of the stem may become affected, while 

 the other side with one or more vascular bundles still normal may con- 

 tinue to provide moisture and food for the living portion of the head. 

 Usually, however, especially in dry weather, the infection is restricted 

 to the head; and most commonly only a part of the head is destroyed. 

 This may be the upper, middle, or lower part, depending on the kind 

 and point of infection. Infection of the rachis causes blighting or dying 

 of the whole head above the point of infection. In such cases the dead 

 spikelets shrink and become more closely appressed to the rachis, while 

 the uninfected portions of the head continue their normal development to 

 maturity and become robust, with spikelets well filled, thus making the 

 difference between infected and uninfected parts still more striking. 



The point of infection, even when the attack is in an advanced 

 stage, can easily be located, especially if the weather has been favorable. 

 It is usually covered at first with a short, cottony, slightly pinkish 

 fungous growth, while the rest of the infected area remains free from 

 such a growth. Later, if the weather is favorable, this growth extends 

 farther over the infected area and becomes the substratum on which a 

 layer of conidia develops. This layer of conidia may be smooth (pion- 

 notes) or more or less granular (sporodochia) , depending on the causal 

 organism and the age of the infection. The older it is the smoother it 

 becomes. The conidial masses, which were originally slightly pinkish, 

 now become dark salmon to grenadine in color, depending on the causal 



