5° 2 
Journal of Agricultural Research 
Vol. XXI, No. 7 
spots resembling leafspot of tomato, while an equal number of horse nettle 
plants not inoculated but kept in the same environment as the inocu¬ 
lated plants remained healthy. During the winter of 1919-20 more than 
500 horse nettle seedlings 1 to 5 inches high were inoculated with this 
fungus, and as many more were used as controls. The leaves of about 
90 per cent of the inoculated plants became infected, but not one of the 
control plants showed any symptoms of the disease. 
The culture used in making these inoculations was isolated from a 
Septoria spot on a tomato leaf and had been used to infect several 
thousand tomato seedlings. In morphology, in growth on standard 
culture media, and in development on tomato leaves it was typical for 
Septoria lycopersici. 
The horse nettle leafspots (PI. 99, A) when small were usually some¬ 
what circular in outline and brown in color, but when older they became 
more irregular in outline, light-colored in the center and dark at the 
margins. There is a larger percentage of circular spots in Plate 99, A 
(artificially infected leaves) than in Plate 97, A (naturally infected 
leaves); but this is due largely, if not wholly, to the fact that the spots 
in Plate 99, A, are younger than those in Plate 97, A. The larger spots 
in both plates are more or less irregular in outline. In fact, the shape 
of the spots on tomato leaves (PI. 98, A) varies from a circular form 
when small to a more or less irregular outline when large. 
The horse nettle seedlings were not quite so susceptible to the leafspot 
fungus {Septoria lycopersici) as tomato seedlings. They showed more 
individual variation in resistance but became infected readily and became 
fairly thickly covered with spots (PI. 99, A). 
The spots on the horse nettle leaves infected in the greenhouse dif¬ 
fered somewhat from those on the tomato leaves in pycnidia production. 
Pycnidia appeared on nearly all the spots on tomato leaves but only 
on a relatively small percentage of the spots on horse nettle leaves. 
They were usually numerous on this small percentage of horse nettle 
spots but were more deeply imbedded than on tomato leaves and were 
not always easily seen without the aid of a hand lens. The appearance 
of both the spots and pycnidia on tomato and horse nettle leaves may 
be seen in Plates 97, B; 98, B; 99, B, C. 
The pycnidia on the horse nettle leaves produced innumerable spores 
which where indistinguishable from those taken from tomato leaves. 
Both the pycnidia and spores in mass are shown in a section of horse 
nettle leaf in Plate 99, B, C. Many of the pycnidia were even more 
deeply imbedded than the pycnidium shown in Plate 99, B, which in 
surface view was not very conspicuous to the unaided eye. 
Since pycnidia of Septoria lycopersici developed rather sparingly on 
horse nettle leaves in the greenhouse, 222 horse nettle plants inoculated 
with a culture of S. lycopersici obtained from tomato were planted 
outdoors where the air was supposedly drier; but only a few scattered 
pycnidia developed on these plants until nearly the end of the growing 
