164 DESTRUCTIVE INSECTS OF VICTORIA : 



of linseed oil. Sometimes raw oil was used and sometimes boiled ; 

 there appeared to be no great difference in result, but if more covers 

 were to be oiled preference would be given lo the boiled. Raw oil 

 without turpentine was applied to a number of covers ; exposure to 

 the sun for several weeks was required to dry these, and then the cloth 

 was found to be not only stiff but very weak, slow combustion 

 apparently having taken place. The oiling of the covers increased 

 their weight by two-thirds without, of course, adding anything to the 

 strength, besides it invariably stiffened the fabric to some extent, thus 

 making it less easy to handle, and more likely to tear. These objections 

 to oiling the cloth might not be serious if the covers were always to be 

 used on well-grown trees, and by experienced hands ; but they proved 

 decidedly serious where the covers were employed in treating mis- 

 shapen, long neglected trees by parties with little or no previous 

 experience. Our need was soon clearly seen to be covers combining 

 the maximum of strength and pliability Avith the minimum of weight. 

 The necessity led me to experiment withunoiled covers of heavier cloth, 

 and after several weights were tried, what is known as No. 10 Ameri- 

 can duck was adopted for large covers, and No. 8 for small ones. For 

 several months, however, the lighter cloth, No. 10, has been used for 

 both large and small sizes. Different brands of this cloth are sold, but 

 only the most closely-woven ones are adapted to our purpose. It 

 weighs between fifteen and sixteen ounces to the square yard, and after 

 it is well shrunk with water no interstices should be apparent when it 

 is held between the eye and the sun. The sewing is done by machine 

 with Singer Company's linen thread, single seam for tent covers and 

 double for sheets ; a short stitch is advisable, and No. 45, or heavier 

 thread, should be used for the sheets. It was found difficult to manipu- 

 late sheet covers of oiled cloth fifty feet in diameter, but even new hands 

 have had no trouble in managing fifty-seven foot sheets of No. 10 duck 

 unoiled. In only one respect are the oiled covers superior to the 

 stronger and more durable unoiled ones, and that is with respect to 

 their gas-retaining properties. The gas escapes through even the oiled 

 cloth, but much more rapidly through the unoiled, even though the 

 latter appears equally tight to the eye. Despite of this effect, however, 

 covers of the unoiled heavy cloth have given far greater satisfaction 

 and will probably continue to be used. But observation of the results 

 obtained by use of the customary dose of one ounce of cyanide to 300 

 cubic feet of enclosed space (for red scale) has convinced me that 

 allowance must be made for the loss of gas by diffusion through the 

 covers. It is observed that the proportion mentioned cannot be relied 

 on to destroy all the scale on small trees when the unoiled covers are 

 employed. A larger dose is advisable even under heavily-oiled covers, 

 while for use with the unoiled, I am of opinion that the proportion 

 should be gradually increased from one ounce to 300 cubic feet for a 

 tree sixteen feet in height, to one ounce to 125 cubic feet for a tree six 

 feet in height. The surface through which the gas escapes increases 



