440 Journal of the Department of agriculture. 



larger sizes are now on sale. Only one machine, so far as is known to 

 the writer, has been imported into South xVfrica. It is a Standard, 

 the price for which iu 1920 was 250 dollars in New York. The 

 American price for the Junior four years ago was 125 dollars. 

 Purchases may be made of the Braun Corporation, Los Angeles, 

 California, or from the New York firm mentioned in connection with 

 cyanegg in the second section of this article. The advent of the 

 cyanofumer marked a very distinct step forward in Californian 

 fumigation ; but many circumstances will probably long tend to 

 retard the adoption of machine generation of the gas in South Africa. 

 The initial cost of a machine is not the greatest obstacle. The 

 difficulty of effecting repairs and replacements on the farm and at 

 such a great distance from the makers is more serious. 



The Senior Entomologist, Capetown, Mr. C. W. Mally, experi- 

 mented with liquefied hydrocyanic acid gas for plant fumigation 

 and advocated its use for this purpose before the idea of employing 

 it was developed in California ; but the conditions for getting the 

 liquid prepared and used were very favourable in California while 

 the reverse here. Commercial production of the liquid was speedily 

 perfected in California, and satisfactory apparatus soon evolved for 

 injecting the liquid under the cover, where it instantaneously 

 volatilizes. The gas is generated in great closed retorts in open-air 

 factories, run through chilled pipes to convert it to liquid, and then 

 packed in special drums for transport to the orchard. The liquid is 

 highly volatile and, being intensely poisonous, immense care has to 

 be exercised in all operations with it. The railways refuse to transport 

 it, and it is conveyed by motor-trucks fresh from the factories to the 

 orchards, where it is used practically at once. Under the Californian 

 conditions, comprising great stretches of well-kept citrus plantations 

 along tar-surfaced motor roads, the liquefied gas has proved a great 

 boon to the f umigators ; but many dithculties, experienced only in 

 minor degree, if at all, in California, will have to be overcome before 

 the liquid can be brought into commercial use for orchard fumigation 

 in South Africa. However, a company to prepare the liquid has 

 been formed at Capetown which hopes to supply it in hermetically 

 sealed glass tubes or flasks at a price which fumigators can afford 

 to pay. The filled glass is to be packed in material that will render 

 the gas harmless should breakage occur, and therefore the railway 

 department is not expected to raise any objection to transporting it. 

 The one or more tubes containing the quantity which is decided to be 

 requisite for the tree is to be placed in a special generator of simple 

 design and the glass crushed by a simple device when all is ready. 



Kinds of C overs. --Tvi'o types of cloth covers, sheet covers and 

 dome covers, are used for fumigation. Sheet covers are flat covers 

 designed to envelop trees as a wagon-sail envelops a load of goods. 

 They may be used for large and small trees, and in California have 

 entirely superseded dome covers. In shape they are made a regular 

 octagon, any waste in cutting the cloth being thus avoided. One will 

 cover as large a tree as will a square sheet of the same diameter, while 

 it needs only five-sixths as much cloth. It is helped over the tree by 

 two long poles, one hooked into a ring tied near the front of the sheet 

 on each side thereof. Dome covers are shaped like the crown of a hat, 

 that is, they have a cylindrical base surmounted by a rounded lop. 



