3°6 
Journal of Agricultural Research 
Vol. I, No. 4 
SYMPTOMS OF THE DISEASE 
So far as has been observed nursery blight affects only the leaf blade, 
but infections occur from early spring well on through the season, so 
that under conditions favorable to the development of the disease the 
young trees have little opportunity for growth. Generally the first 
indications of infection appear in the form of minute roundish spots, 
which are dark reddish brown on the upper leaf surface and blackish 
on the lower. (PI. XXXVII, Fig. C.) These slowly increase in size 
until a diameter of 2 to 5 mm. is often reached in the individual 
spots. With increase in size the center of the spot on the upper surface 
assumes an ashen-gray color, which is usually bordered with reddish 
brown, while the lower surface remains black throughout or with an 
occasional tiny ashen-gray spot in the center of this dark-colored area. 
(PI. XXXVII, Fig. /.) The gray color in both cases is caused by a rais¬ 
ing of the epidermis, thus leaving an air space between it and the tissues 
Fig. i.—C ross section of pecan leaf recently infected with the nursery-blight fungus (Phyllosticta caryae 
Peck) from pure culture. X260. 
below. The leaves are often considerably peppered with these spots, 
and by their coalescence larger areas are often involved. Very fre¬ 
quently the spots elongate and coalesce along the midrib and larger 
veins, thus giving a very characteristic appearance. The parenchyma 
cells and vascular bundles are often killed and discolored over large 
areas. Whenever the vascular tissue becomes involved to any great 
extent the supply of water is cut off from below and the leaf soon dries 
up and falls. Figure i shows the microscopical appearance of the 
diseased cells in a recently infected leaf. 
MYCOEOGICAE AND PATHOEOGICAE STUDIES 
Isolation of the Fungus 
Rough microscopical examination of a considerable range of diseased 
material disclosed no fungous or bacterial form which was at all con¬ 
stantly associated with the symptoms. Occasionally a tiny thin-walled 
pycnidium was encountered, but no spores were found and usually no 
fungous mycelium or fruiting body of any kind. Cultures made during 
1910 and 1911 from material several days old gave only saprophytic 
fungi as shown by the negative results of all the inoculation tests. 
