July i, 1921 
Relation of Horse Nettle to Leaf spot of Tomato 
503 
season. They were then found chiefly in small, dark brown spots lying 
in large dead areas near the tips and edges of the leaves. As pycnidia 
did not appear on tomato leaves in the field until very late in the fall, 
it is quite possible that the very wet weather during August hindered 
their development on both tomato and horse nettle. In fact it has been 
repeatedly noted while working with this fungus, both in the greenhouse 
and in the field, that the development of pycnidia on tomato plants is 
favored by dry air and hindered by moist air. This variability in sporu- 
lation occurs also on culture media. The drier areas in corn meal cul¬ 
tures of 5. lycopersici develop pycnidia readily, while those that are 
moist produce them only after the medium becomes somewhat dry or 
not at all. 
INOCULATION QF TOMATO AND HORSE NETTLE SEEDLINGS WITH SEP- 
TORIA LYCOPERSICI REISOLATED FROM HORSE NETTLE LEAVES 
Thirty young tomato plants and 14 young horse nettle plants 3 to 6 
inches tall were inoculated by spraying their leaves with spores of a 
culture of Septoria lycopersici reisolated from horse nettle. Twenty 
uninoculated tomato plants were sprayed with distilled water and used 
as controls. Both the inoculated plants and the control plants were 
kept in a moist chamber 60 hours. 
All the tomato and horse nettle plants became heavily infected, but 
none of the controls developed any symptoms of the disease. Pycnidia 
developed on the spots, but they were much more common and more 
conspicuous on the tomato than on the horse nettle. The spores, which 
developed in profusion, were identical in shape and size with those pro¬ 
duced by the original culture obtained from tomato. 
septoria on naturally infected horse nettle 
Spots resembling leafspot of tomato began to appear on horse nettle 
leaves at the Arlington Experimental Farm and in fields and gardens in 
the vicinity of Washington about the middle of August but bore very 
few if any pycnidia before the middle of September. This was approxi¬ 
mately coincident with the appearance of pycnidia of Septoria lycopersici 
on tomato leaves. 
The pycnidia found on naturally infected horse nettle leaves after the 
middle of September were rather numerous but appeared on only about 
1 per cent of the spots. They contained innumerable spores that were 
indistinguishable morphologically from those of the tomato leafspot fun¬ 
gus, Septoria lycopersici. Dead areas near the tips and margins of the 
leaves seemed to afford the most favorable conditions for their develop¬ 
ment, for they were found most frequently within these areas. 
Several attempts were made to isolate a pure culture of the Septoria 
from naturally infected horse nettle leaves by use of the spores, but in 
each case the spores failed to germinate. The writers were not surprised 
at these results, however, as it often requires repeated efforts to isolate 
