FUMIGATION OF CITRUS TREES. 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 
