198 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



jacket, our common wasp, which is so injurious to fruit, and 

 which makes its nest in the ground, is easily killed by this sub- 

 stance. The nest is located, and about dark, when the wasps are 

 all in, about an ounce of carbon bisulphide is poured down the 

 hole, and a handful of earth thrown over it to keep the vapour 

 in. By morning all will be found to be dead. Ants' nests can 

 be destroyed in the same way. Carbon bisulphide is also one of 

 the best remedies for gophers. If used in the fall, after the 

 rains have begun (so that the ground is not too porous), an ounce 

 poured over a rag and stuffed into a hole and covered with earth 

 will destroy the inmates. 



Hydrocyanic Acid Gas. — This is practically the only acid 

 which is strong enough to kill the insects on a tree with safety 

 to the leaves, and within [a short time enough to make its use 

 practical on a large scale. Its work is very effectual and satis- 

 factory, but it is very expensive, and, therefore, is only available 

 for the more profitable trees, such as the citrus varieties. It 

 may also be used for disinfecting. The gas is extremely 

 poisonous, and, sometimes, for reasons not entirely understood, 

 is very injurious to the foliage ; but the injury is almost all pre- 

 vented by its use at night. The process is to cover the tree with 

 a tent of sail-cloth, oiled to make it tight, and in a vessel 

 beneath the tent the chemicals which make the gas are placed. 

 After half an hour the tent is removed and put over the next 

 tree. The chemicals needed for every 100 cubic feet are ^ 

 ounce of potassium cyanide, § ounce of water, and J ounce 

 of sulphuric acid. The common practice in California is to use 

 it decidedly stronger for small trees and weaker for the largest 

 trees. In the smaller trees it is safe to use it stronger, as the 

 small amount of gas used is very quickly diffused. When it is 

 produced in large quantity, as is necessary for a large tree, some 

 of the gas, scarcely at all mixed with air, may come in contact 

 with the leaves and injure them. The practice probably arose, 

 in part, from some tables which have been published widely in 

 California, where the contents of the tent was calculated by 

 multiplying the height of the tree by its breadth. The practice 

 is not justifiable, and if the weaker amount is successful there is 

 no reason for not using the same proportion on smaller trees. 



There are many kinds of tents used, and many plans for 

 changing them from tree to tree, the details of which we cannot 



