72 P:XPEU1MENT station. [Jan. 



which each factor may play. The experiments of Dr. Feruald 

 and ^lessrs. Tower and ,llooker, already referred to, were not 

 all made at the same time, which unfortunately introduces a 

 varying factor. They observed that drops of water on the 

 foliage caused burning. Burning often results from fungicides 

 remaining in a liquid form for even a brief period on the foliage. 

 Water apparently absorbs hydrocyanic acid gas, since we have 

 found that trout, which are very susceptible to this gas, located 

 in an aquarium outside the compartments in greenhouses being 

 fumigated with this gas, are killed, although goldfish do not 

 seem to be affected. 



While these experiments do not throw liglit on all the factors 

 involved in susceptibility to burning, they do demonstrate that 

 burning by fumigation with hydrocyanic acid gas is induced 

 by a difference in the development of the tissue, whether brought 

 about by inferior light conditions or excessive moisture in the 

 soil, the more poorly developed tissue being more susceptible 

 to burning. Further experiments are being conducted in our 

 laboratory to throw more light on the influence of other factors 

 on burning. 



The most important practical feature brought out by these 

 experiments is that fumigation should be done only when the 

 plants are in the right condition. Any expert gardener can de- 

 termine at a glance whether his plants are develojiing normally, 

 and under glass he can control the environment to a large extent. 

 Care should be used in fumigating during periods of cloudy 

 weather, as under these conditions the same amount of resistant 

 tissue is not developed. Low night and day temperatures, as 

 well as a decrease in the soil moisture, counteract this to some 

 extent, but the presence of light is the most important factor 

 in developing resistant tissue. Fumigation will caus(» less in- 

 jury following bright than cloudy weather, and should not be 

 done for two or three days after a cloudy period, so that the 

 plants will have a chance to harden up their tissue. Plants 

 growing in relatively dry soils are affected to a less degree by 

 fumigation than those in moist soils. The same care and atten- 

 tion should be given to prevent injury from fumigation that is 

 used by lettuce growers to prevent topburn. 



