THE TREATMENT OF INSECTS AND FUNGI IN THE UNITED STATES. 197 



buted. If not so diluted, care must be taken not to apply it so 

 thickly in places as to endanger the foliage. 



Gas Tkeatments. 



Gases have the property of diffusing themselves with 

 great rapidity, so that when applied in a closed space every 

 part of that space will in a short time contain some of the 

 gas. Thus no other method of killing insects is calculated to be 

 as thorough in its work. But in an open space this property of 

 diffusing destroys, to a great extent, its utility. Sulphur applied 

 as a powder, as has already been stated, is not effective until it 

 becomes a vapour ; and then the dissipation is not as much as 

 with most gases, because of the weight of sulphur vapour and the 

 fact that it is applied over whole fields at once. The imprac- 

 ticability of enclosing most cultivated plants, and the cost of the 

 treatment, both in time and chemicals, makes the method 

 useful to only a very limited extent. We recommend but two 

 gases. 



Carbon Bisulphide. — This substance is not available for 

 plants in active growth, and is chiefly useful for stored products, 

 such as seeds and grains. It can be used for disinfecting soils 

 and ridding other articles of insects. In disinfecting soils an 

 injector is used. A number of forms of the latter are on the 

 market in Europe, where phylloxera eradication has required 

 them. It is doubtful if this method of soil disinfection would be 

 profitable in the United States for the destruction of any insect. 

 For destroying insects in seeds or grain, carbon bisulphide is a 

 very cheap and satisfactory means. The bin or box containing 

 the seeds to be disinfected should be tight, at least at the sides 

 and below. A dish is placed on top of the material to be treated, 

 and a quantity of the carbon bisulphide poured in. It evaporates 

 rapidly, and the vapour, being heavier than the air, sinks into the 

 lower part of the bin. The top should be covered also, in order 

 that the vapour may remain a long time in the grain. Very 

 rarely will bins be perfectly tight, so that the exact amount 

 necessary cannot be stated. Usually the estimate is made at one 

 pound to the ton of grain, which is sufficient for a fairly tight 

 bin. Grape vine cuttings are most successfully disinfected in a 

 similar way, by placing a saucerful of the bisulphide on the cut- 

 tings in a tight box, and leaving for forty minutes. The yellow 



