A SERIOUS LETTUCE DISEASE. 
115 
certain tliat this estimate does not fully represent the actual number 
formed under conditions of badly infected beds. 
TABLE VIII.—SHOWING DISTRIBUTION OF SCLEROTIA IN THE PLANT. 
Sclerotia can be grown upon a great variety of media but upon 
some media they do not develop in any large quantity. They were 
formed upon the surface of the lettuce broth cultures after the my¬ 
celium had grown to a considerable extent, thus forming a support 
for them; but sclerotia have never been seen to form within the 
liquid medium itself and plants brought into the laboratory and kept 
in culture dishes where they became very wet did not form as many 
sclerotia as those placed upon soil in the greenhouse where the plants 
were less wet. 
In a test of plain agar, plain agar plus 1 per cent, glucose, plain 
agar plus 5 per cent, glucose, plain agar plus 1 per cent, peptone, 
plain agar plus litmus-lactose, plain agar plus 1 per cent, starch and 
lettuce agar, it was seen that sclerotia formed in all the media except 
those which contained peptone or litmus-lactose. In a test of tempera¬ 
ture relations no sclerotia developed in the higher temperatures, above 
twenty-six degrees C.; nor at the lower temperatures, below eight de¬ 
grees C. The formation of sclerotia is inhibited by these extremes 
before the growth of the mycelium is stopped. 
Two cultures of Sclerotinia upon the corn meal saturated with apple 
juice, in 20 cm. culture dishes, were inoculated January 17, 1907, and 
the first mature sclerotia were picked from these cultures on January 
28th, 11 days from inoculation. 
From these cultures full size, black sclerotia w r ere taken every alter¬ 
nate day until February 8tli, then every third day until February 17th; 
a period in all of one month from the date of inoculation. During 
this time one of the cultures produced 523 sclerotia and the other 
397 or a total of 920 for the two cultures. The following table shows 
the number of sclerotia taken on each dale. 
