FUMIGATION. 165 



in proportion to tlie space enclosed as the dimensions of the tree 

 decreases ; hence the necessity for givino; small trees proportionately 

 greater doses. Tliere is more than fonr times as much surface to the 

 space encompassed by the cover in the case of a 4' x 3' tree than 

 there is in one 16' x 12'. When trees are dosed with the quantities of 

 chemicals recommended in the old tables, there is little odour of the gas 

 under the two smaller sizes of tent-form covers forty minutes after the 

 reaction has taken place, while under the large sheets it is often dis- 

 agreeably strong ninety minutes after, thus clearly demonstrating the 

 error of basing the table of quantities on the cubic contents alone. A 

 number of covers of a Willesden rot-proof and water-repellant duck of 

 the same weight and quality as the ordinary I^o 10. duck have been 

 tested, and have been found to better retard the permeation of the gas. 

 though not to a very marked extent. The cloth Avas less easily sewed 

 than ordinary duck, and its odour of ammonia when handled in the 

 making gave much annoyance to the parties Avho sevved it. The 

 naturally green colour faded quickly under the action of the cyanide 

 fumes. It is yet too early to decide definitely whether or not it is pre- 

 ferable to the ordinary cloth in the long run. The cost in London was 

 about equal to what is paid for the other in Cape Town. Several 

 parties are using covers of oiled unbleached calico and express them- 

 selves well satisfied. Dressing a cover with fat, as waggon sails are 

 Avaterproofed, was tried by the manager of the Oudtshoorn outfit and 

 found inadvisable ; the dressing never dried and soon Aveighted the 

 cover with an accumulation of adhering soil and rubbish. 



Manipxdation of Sheet Covers. — The stylo of uprights for raisincr 

 and lowering the sheet covers described in the " Gas Treatment " 

 pamphlet is still employed, but the long poles are now tapered from 

 2^" X 4" at the base to 1^" x 4" Jtt the top, and are twenty-six feet in 

 length, and the braces are cut six feet instead of five ; a simpler device 

 finds a few champions among orchardists working Avith a single sheet. 

 The idea is to gather half of the sheet in loops of rope and by means 

 of poles as levers to raise this gathered half until it is directly above 

 the tree to be covered, Avhile the loose half hangs to the ground ; then 

 to slaken the loops and thus permit the suspended folds to open and 

 fall forward. Two long light poles, pointed at the base and at least 

 three feet higher than the tallest tree to be covered, two pulley blocks, 

 and a quantity of rope is all the apparatus required. Two small holes, 

 about the Avidth of the tiees apart and in line with, and equally distant 

 from the centre, are cut in the sheet ; the tops of the poles are passed 

 a fcAv inches through the holes and are bound securely in this position ; 

 one end of a long rope is then fastened to the projecting top of the 

 pole, and the other passed out around the margin of the sheet back to 

 the pole beneath the hole, and through a pulley block there secured. 

 When these tackle ropes are adjusted to both poles, half of the sheet 

 lies in two loops, and hauling on the free ends of both ropes contracts 



