Feb. 5, 1917 
Leafspot-Rot of Pond Lilies 
229 
although somewhat more slowly, when inverted leaves are inoculated 
on the morphologically lower surface, although stomata are present 
only on the upper surface. 
The usual occurrence around the developing spot of a pale yellowish 
green halo grading off to the normal green of the leaf has been noted 
previously (PI. 67,^; 68, C). No mycelium has been found in this 
bordering tissue; and even if sometimes present in the intercellular 
spaces, it is almost certainly not intracellular. From these facts it is 
evident that some product or products of the fungus metabolism are 
capable of diffusing into, injuring, and finally killing the host cells. 
The epidermal cells in sections of healthy leaves stained with Flem¬ 
ming’s triple stain (PL 70, A) are seen to be free from coagulation 
products, the nuclei are clearly differentiated, and the numerous chloro¬ 
phyll bodies are well rounded out and definite in outline. In the infected 
areas even at so short a time as three to four days after inoculation 
the epidermal cells are frequently filled more or less completely with 
coagulation products, the nuclei are disintegrating, and the chlorophyll 
bodies are fewer in number, and those left are seen to be disintegrating 
(PL 70, B, C). The diseased parts of the leaf take the orange stain more 
readily, while the healthy parts show a decided affinity for the gentian 
violet. These differences can not be due to variations in individual 
leaves nor to differences in microtechnic, for where sections have been 
made through the edge of a young spot into normal tissues beyond it, all 
these differences have been seen in a single section. 
Conidia have been found in one or two cases on freshly collected 
material and have developed twice on the upper surface of leaf spots in 
a damp chamber. Usually, however, after the removal of diseased leaves 
from the water and after they had been placed in a damp chamber, a fine 
whitish growth of more or less erect hyphae develops over the infected 
areas without the formation of conidia. In several instances sclerotia 
have developed on the leaf spots after the leaves have been placed in a 
damp chamber. 
The fact that infections have not been found to occur regularly on 
submerged leaves is probably due in part to a lack of sufficient oxygen, 
since in liquid and solid media growth of the fungus is almost entirely 
limited to the surface. 
TAXONOMY AND DESCRIPTION OF FUNGUS 
This pond-lily parasite belongs to the hyphomycetous group of the 
Fungi Imperfecti. It is to be included in the family Dematiaceae among 
those forms with dark, loose hyphae and conidia, but without definite 
stromata or fruiting bodies. The elongated, transversely septate, more 
or less helicoid conidia place it in the genus Helicosporium belonging to 
the small group Helicosporae. Of the two other genera in this group, 
Helicopsis is without definite mycelium and Helicoma bears muriform 
conidia. 
