Forcing-House Miscellanies. 411 



rose from a watering can, the stem of the funnel being set in the 

 soiL The plants remained covered with enamel cloth nearly two 

 hours, which sufficed to kill all the insects, and did not injure the 

 violets, these being the plants treated. 



Hydrocyanic gas — The success which has followed the use of 

 hydrocyanic gas in the treatment of scale insects infesting the 

 orange groves of California has suggested the idea of its possible 

 value in destroying greenhouse pests. The common method of 

 making the gas is as follows : One iiuid ounce of sulphuric acid is 

 added to 3 ounces of water. To this diluted acid there is then 

 added 1 ounce of 60 per cent, cyanide of potassium. Effervesence 

 immediately takes place, and the gas is freely given off. The 

 quantities here given are sufficient for a space containing 150 cubic 

 feet, the plants being exposed to the gas for 1 hour. When trees 

 are dormant such treatment is not followed by any evil effects. 



During the past spring several growing plants were exposed to 

 the action of the gas when used according to the above directions. 

 Tomatoes, egg-plants, oranges and roses were used. The day fol- 

 lowing the treatment showed that all the plants were injured, but to 

 what extent could not well be determined. After two weeks had 

 passed, however, the effect of the treatment was plainly seen. The 

 tomato plant died ; the egg-plant and the rose lost all their foliage, 

 but fresh leaves were appearing on the stems ; the orange suffered 

 the least, since only the young leaves were affected. The mites had 

 all been killed, so that in this respect at least the experiment was 

 successful. 



Other trials were made with the gas, using the same kinds of 

 plants, but it was found to be impossible to destroy the mites with- 

 out injuring at least some of the plants. The use of hydrocyanic 

 gas for the destruction of greenhouse pests can, therefore, scarcely 

 be recommended. It should also be remembered that this gas is 

 very poisonous. 



Sulphur is an element which is of the greatest service in green- 

 house work. It is an invaluable agent for the destruction of mil- 

 dews, and is also of great assistance in overcoming red spider. As 

 commonly used, it is mixed with an equal bulk of air-slaked lime 

 or some similar material, and then water, oil, milk or some other 

 liquid is added until a thick, creamy paste is obtained. This is then 

 painted upon the heating surfaces in the house, and the sulphur 

 fumes are given off. The same result can be obtained much more 



