10 
WALTER SPURGEON BEACH 
small, and Sonchus oleraceus was a very uncongenial plant for the fungus. 
The comparison will be more clear with a description of the spots. 
Septoria lactucicola produces upon L. canadensis round, reddish-brown 
to black spots, usually from 3 to 15 mm. in diameter, and frequently with 
concentric zones of lighter and darker color. L. scariola was the only new 
host in which these characters were preserved, and here the spots were 
lighter-colored, probably on account of the thinner leaves. Upon L. sativa 
the spots were spreading, with an indefinite border, and several times 
larger than those on L. canadensis where the border is very definite. They 
were colored light brown in the center, gradually changing to yellow and 
then to the green of the normal tissue. No pycnidia were observed in the 
greenhouse, but they developed in two days upon leaves detached and 
put into a moist chamber. For a further comparison of the spots on these 
first three hosts compare Plate I, figures 7-9. The spots upon Prenanthes 
sp. were i mm. to 3 mm. in diameter, dark brown, more or less angular, 
and usually surrounded by a greenish-yellow zone. Pycnidia were seen 
upon the plant, but spores developed only in the moist chamber. The 
spots upon Sonchus oleraceus were i mm. to 5 mm. in diameter, grayish 
brown, and more or less limited by the leaf veins. A small number of 
pycnidia with spores characteristic of Septoria lactucicola were obtained 
upon two of several infected leaves placed in a moist chamber. 
That the biologic characters change with the host is clearly shown. 
Such variation has doubtless led to erroneous determinations, or to the 
useless multiplication of species in many instances. Environment may 
likewise cause alterations of these characters, for the spots on L. canadensis 
tended to lose their concentric zones and become spreading if kept long in a 
moist atmosphere. 
Septoria lactucae Pass. 
The following hosts are reported for Septoria lactucae: Lactuca sativa, 
L. scariola, L. virosa, L. canadensis, and Chrondrilla muralis. The fungus 
appears to cross readil}' between L. sativa and L. scariola, and causes upon 
both of these hosts marked disease. The passage of the fungus from, either 
of these hosts to L. canadensis apparently takes place only under very 
favorable conditions of heat and moisture, for it was necessary to cover the 
plants for a prolonged time with bags, and to atomize them frequently 
with water to secure infection. A considerable degree of infection was 
secured in this way, yet it is probable that this Septoria does not occur 
commonly on L. canadensis in nature. The disease characters on L. canaden- 
sis were different from those seen upon L. sativa or L, scariola; the spots 
were smaller, had no tendency to spread, were darker in color, and commonly 
had a yellow zone for a border. They were angular in outline, usually i 
mm. to 5 mm. broad, and the central area was brown to black. Pycnidia 
and spores were present. 
