26 



It should be remembered that hydrocyanic-acid gas is one of the deadliest poisons 

 known, fatal to human beings and plants as well as to insects. 



Greenhouses which are within 50 to 75 feet of dwellings should not be fumigated 

 unless the windows and doors of the latter on the side next to the greenhouse can be 

 closed during the operation. 



The bag containing the cyanide should not be permitted to drop into the jar until 

 the operator has left the house. 



It is essential that the exact proportion of cyanide be used at the rate designated for 

 each cubic foot of space and that the exposure should not exceed the limit ascertained 

 by experiments as appropriate to the plants to be fumigated. A greater strength of 

 gas or a longer exposure than specified is apt to result in injury to the plants. 



It is best to use this method at first experimentally on a small scale before attempt- 

 ing the fumigation of an entire greenhouse, and a preliminary test should always be 

 made in case plants of a species or variety not previously fumigated are to be treated. 



Concerning the possibility of hydrocyanic-acid gas forming a deposit 

 upon any of the substances with which it might be brought in contact 

 in its ordinary use as a fumigant, either in greenhouses or in build- 

 ings infested by indoor insects, Dr. H. AY. Wiley, chemist of the 

 Department of Agriculture, states that there is no possibility what- 

 ever of such a contingency, unless the gas comes in contact with some 

 alkaline bod}', such as soda or potash, with which it would form a 

 salt. The soluble cyanides are extremely poisonous, and if this gas 

 were to act upon lye, or any similar alkaline body, a certain amount 

 of cyanide would be produced. In a dry room, in the absence of 

 alkaline bodies, there could not be any possible danger of a poisonous 

 body being formed. 



THE VIOLET SAWFLY. 



(Emphytus canadensis Kby. ) 

 RECENT INJURY. 



October 19, 1897, Mr. Dorsett brought to this office specimens of 

 the larva? of this sawfly with the information that they were injuring 

 yiolets in his greenhouses at Garrett Park, Md. He had experienced 

 great trouble with this pest and stated that Mr. Joseph Markle, of 

 Rhinebeck, N. Y., was similarly annoyed by its presence on green- 

 house yiolets. Later Mr. W. G. Saltford. of Poughkeepsie, X. Y. . 

 sent specimens of the larva? to this office, and Mr. B. T. Galloway, of 

 this Department, also submitted for identification another lot of larva? 

 from Garrett Park, Md. From material received from Mr. Dorsett 

 the adult was reared, and from the bred lot a number of observations 

 on the development of the species were made and will be here recorded. 



January 12, 1900, Dr. James Fletcher reported attack by the larva? 

 of this insect during the previous year in the extensive violet houses 

 of Mr. J. H. Dunlop. of Toronto. He stated also that it was a com- 

 mon pest at Ottawa on pansies and some species of violet. 



