FUMIGATION OF CITRUS TREKS. 17 



cactus juice combined with linseed oil, or glue, or tannin, etc. Expe- 

 rience with these many substances has resulted in discarding all of 

 them' in this State, so that to-day no effort is made to render tents 

 gas-tight by the use of any liquid substance. 



It is well known that a decidedly smaller dosage would be required 

 with gas-tight covers than is nesessary with tents of the present 

 character. This has led many writers on fumigation to advise the 

 treatment of the cloth with some of the substances just mentioned to 

 accomplish that end. Had these writers undergone a considerable 

 experience in the actual handling of tents in the field their expressions 

 on this particular subject might have been somewhat modified. 

 Tents treated by some of these methods will be rendered gas-tight, or 

 nearly so, but for certain practical reasons they are not now used and 

 never will be used on a large commercial scale. 



Experiments have been made with many different substances in 

 attempting to render cloth gas-tight, and several samples of gas-tight 

 or almost gas-tight cloth have been received from dealers. This 

 experience in all cases has shown that to render a cloth very much 

 more nearly gas-tight than is possible in weaving, some treatment 

 must be used which materially increases the weight of the tent as 

 well as rendering it somewhat stiff. Both of these conditions should 

 be avoided as much as possible. Heavy tents are not only difficult 

 to manipulate, but also destroy fruit and break branches while being 

 hauled over trees. Stiff tents will not lie close to the ground, thus 

 allowing the escape of gas. Tents must be constantly overhauled to 

 mend the holes which result from acid burns as well as other causes. 

 The mending of such treated cloth is so difficult as to be impracticable, 

 especially in large-sized tents. 



After considering both sides of the question experience leads to 

 the conclusion that the economy of gas resulting from gas-tight tents 

 is more than offset by the many difficulties experienced in the use of 

 such stiff heavy covers in the field . The writer advises the purchase 

 of the most closely woven untreated cloth obtainable, of the char- 

 acter and weight previously mentioned (p. 12), believing such to be 

 superior for orchard work to cloths which have undergone a treatment 

 to render them gas-tight. 



Small tents used in treating nursery stock, and especially covers of 

 cloth made over a framework in the shape of a box having one end 

 open so as to be easily placed over nursery trees or such small plants, 

 can be rendered gas-tight without experiencing some of the more 

 serious objections to their practical use that exist in the case of large 

 covers in orchard work. Linseed oil is very suitable for this purpose. 

 The preparation and application of a linseed-oil varnish, which is 

 used by the War Department in the treatment of cloth for balloon 

 purposes, is quoted below. It renders the cloth gas-tight and at the 



