MICHIGAN ACADEMY OF SCIENCE. 
45 
A FUNGUS DISEASE OF GREENHOUSE LETTUCE. 
J. B. DANDENO. 
In a large part of western Michigan, a very destructive disease, com¬ 
monly affecting greenhouse lettuce, renders the production of head-let¬ 
tuce, at times, a not too profitable industry. In some years, thousands 
of dollars’ worth of lettuce has been so injured as to be practically of 
no market value. This disease has been already reported from Michi¬ 
gan and some other states under the name of Marsonia* perforans, 
E&E., but it is not a Marsonia at all for reasons which shall be men¬ 
tioned presently. 
In 1896, in the report of the Ohio Agricultural Experiment station, 
appears a description of the fungus by A. D. Selby, and also Ellis & 
Everhardt’s technical description which reads: “Spots small, irregular 
in shipe, 1-2 mm. in diam., pale soon deciduous, acervuli 100-120 micron 
in diam, or by confluence larger. Conidia abundant, clavate, or wedge 
shaped, hyaline, faintly uniseptate, (11-15)x (2y 2 -3) microns, excep¬ 
tionally reaching 20 microns long.” * * * “Marsonia perforans, 
E&E., n. sp.” Mr. Selby states: “Specimens were sent to Dr. J. B. 
Ellis, who proposes the name Marsonia perforans, E&E., n. sp., for the 
fungus.” Mr. Selby himself proposes the common names Lettuce Leaf 
Perforation. 
The accompanying photography shows the appearance of affected 
leaves and the general habit of the fungus. Even from this, it is quite 
apparent that it is the same fungus as that reported by Mr. Selby, 
though the detailed descriptions differ materially from that given by 
Ellis and Everhardt. 
DescriptionParasitic on leaves of cultivated lettuce,—particularly 
head-lettuce cultivated in greenhouses—; produces brownish spots 
which on the blade become holes, and on the mid-rib elongated sunken 
areas. 
Mycelium ,—septate with numerous septa, sparingly branched, found 
almost wholly on the surface, haustoria entering the cells, but occa¬ 
sionally the mycelium penetrates through the opening of the stomata; 
found typically running in parallel strands. (Fig. 4.) 
Conidiophores,: —short, unbranched, somewhat bottle-shaped (Fig. 2), 
about 15 or 20 microns long, frequently once septate and erect or nearly 
so, bearing one condium. 
Conidia ,—once septate, narrowly obovate, 15x4 microns, generally not 
quite symmetrical, having a tendency towards crescent-shaped, easily 
detached from the conidiophore, hyaline, frequently growing in clusters 
of two to five. (Fig. 2.) 
* Sometimes spelled Marssonia. 
11 am indebted to Professor E. E. Bogue for the photograph. 
