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 dro}) into tlie jar until 

 the operator has left the house. 



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

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

 by experiments as approi:)riate to the plants to he 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. 



Concernino- the possibility of hydrocj^anic-acid gas forming a deposit 

 upon any of the sal)stances with which it might l:)e brought in contact 

 in its ordinary use as a fumigant, either in greenhouses or in ])uild- 

 ings infested b}^ indoor insects, Dr. H. W. 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 w^th some 

 alkaline l)ody, 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, oi- any similar alkaline l)ody, a certain amount 

 of cyanide would l)e produced. In a dry room, in the al)sence of 

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

 body being formed. 



THE VIOLET SAWFLY. 



{Emp]ij/liis canadeiif(i>< Kby. ) 

 RECENT INJURY. 



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

 the larvaa of this sawfly with the information that they were injuring 

 violets in his greenhouses at Garrett Pai*k, Md. He had experienced 

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

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

 house violets. Later Mr. W. G. Saltford, of Poughkeepsie, N. Y. , 

 sent specimens of the larv* to this office, and Mr. B. T. Galloway, of 

 this Department, also submitted for identification another lot of larvaB 

 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 1)e here recorded. 



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

 of this insect during the previous jeav 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. 



