Feb. *4.2933 
Control of LetUice Drop with Formaldehyde 
651 
average growth of 5 mm. Sclerotia exposed 20, 25, and 50 minutes 
showed no growth at the end of 6 days, but at the end of 21 days a few 
sclerotia treated for 20 and 25 minutes showed scant growth. The un¬ 
treated sclerotia produced an average colony growth of 31 mm. 
Nine out of 90 particles of mycelium showed growth (Table II); these 
remained in the solution only 5 minutes and showed no growth until the 
fourth day after they were transferred to the agar. The controls showed a 
vigorous growth at the end of the first day. Colonies from treated par¬ 
ticles of mycelium developed sclerotia more slowly and fewer in number 
than those of the controls. 
One-toTwo-Hundred Formaldehyde Solution. —The method of 
procedure was the same as with the 1-50 solution. *Results taken 6 days 
after treatment showed that sclerotia kept in the solution for 20 minutes 
produced colonies averaging 17 mm. in diameter, while those exposed for 
30 minutes developed colonies averaging 13 mm. Sclerotia exposed for 
greater periods were killed. Colony growth from the sclerotia of the 
untreated lot showed an average diameter of 43 mm. 
Out of 90 bits of mycelium which were treated for different lengths of 
time, as shown in Table II, 18 were treated for 5 minutes. All of these 
developed with retarded growth. Eighteen were treated for 10 minutes, 
14 of which were growing at the end of the fourth day and 18 at the 
end of the eleventh day. Of 18 treated for 15 minutes, none were growing 
at the end of four days, but 12 showed growth at the end of 11 days. 
Particles treated for 20 and 30 minutes were killed. The 18 controls 
showed vigorous growth at the end of the first day. 
EFFECT OF FORMALDEHYDE ON SCLEROTIA AND MYCELIUM AT DIF¬ 
FERENT DEPTHS IN SOIL 
From the practical as well as the scientific viewpoint it is important 
to know to what depth sclerotia and mycelium are killed by a 1-100 
formaldehyde solution applied to the surface of the soil. To determine 
this, sclerotia and mycelium were collected, placed in labeled copper 
wire baskets, and buried in a good lettuce soil at different depths (Table 
IV). Subsequently, the surface of the soil was treated with a i-ioo 
formaldehyde solution at the rate of 1 gallon to the square foot. At the 
end of 7 days the baskets were removed, opened, and 9 sclerotia from each 
depth washed in sterile distilled water and transferred to three nutrient 
agar plates. The particles of mycelium were treated in a similar manner. 
Growth was recorded at the end of the first, second, and third weeks. 
Final results from a large number of tests are recorded in Table IV. 
Infested lettuce soils of commercial greenhouses contain sclerotia and 
mycelium of the causal fungus at varying depths. By the method just 
described it is possible to treat the organism under conditions practically 
the same as those in the soil of commercial houses and still recover the 
organism from the soil at will. 
Table IV shows that with the exception of one particle buried at a 
depth of 16 inches all mycelium down to 20 inches was killed. 
