Nov. 12, 1921 



Plum Blotch 



367 



Wolf found the fungus on the leaves only of Prunus sp. in Texas Their 

 description is as follows : 



Maculis minutis, .5-.8 mm diam., brunneis numerosis, venis limitatis; pycnidiis 

 solitariis in quaque area, 50-125 ix diam.; sporulis globulosis vel leniter elongatis, 

 hyalinis 6-9 m- 



On Prunus sp. Boeme (Texas) 1554 (Type). 



On the upper surface of the leaf are very numerous brown areolae bounded by the 

 veins of the leaf. The lower surface may not be discolored. These minute spots fuse, 

 and each contains at its center a single black pycnidium. The pycnidia contain 

 globular or slightly oval, clear spores. 



Fig. I. — Section through a pycnidium of Phyllosticta congesta, showing spores. Natural 

 infection on plum fruit, Georgia 1917. X 340. 



Heald and Wolf do not mention the fact that the older spots become 

 gray or silvery, though the type specimens as well as those collected by 

 Scott and the writer show this to be the case. The spots on these 

 leaves and those on Georgia specimens collected by the writer show a 

 marked resemblance, and the fungi found upon them are morphologically 

 the same. The spots on the leaves collected by the writer have a greater 

 tendency to fall out. ^iof-:;, 



The pycnidia (fig. i) are glistening, lens-shaped, erumpent, on the 

 leaves 65 to 120 /x in diameter, on the fruit 60 to 120 /x in diameter. 

 On the average, pycnidia on the fruit are somewhat 

 larger than those on the leaves. Spores on the leaves 

 measured 7 to 9 ju in diameter, on the fruit 8 to 9 /i. 

 Spores from younger spots were invested with gelati- 

 nous envelops which were sometimes lengthened into 

 appendages (fig. 2). Spores from older spots do not 

 show these envelops, and they are not to be found in 

 the dried herbarium specimens. The young spores 

 of Phyllosticta solitaria have sucli an envelop. In fact, 

 P. solitaria and P. congesta resemble one another so 

 closely that on purely morphological grounds they 

 might be considered as identical. Since the ascogenous stage of neither 

 fungus is known, the writer prefers to retain the name P. congesta as a 

 matter of convenience, unless it is shown by cross inoculations that the 

 fungus on the apple and that on the plum are identical in every way. 



Fig. 2. — Spores of Phyl- 

 losticta congesta, with 

 the gelatinous envelops 

 which are sometimes 

 present. From pycni- 

 dia on plum fruit, 

 Georgia 1917. X 680. 



