202 DISEASES AND INSECT ENEMIES. 



which must also be considered where tobacco is 

 used. As everyone knows, the odor is exception- 

 ably disagreeable and undesirable. This is par- 

 ticularly the case in violets, which readily take up 

 many foreign odors and never fully recover from 

 the effects. It is therefore found undesirable to 

 pick violets in a house which has been recently 

 fumigated with tobacco. In fact at least a week 

 should elapse after fumigation before any picking 

 is done. These reasons, together with others 

 which have been given, have prompted us to 

 practically abandon the use of tobacco in every 

 form for aphides and insects of this nature. 



A good deal has been written about the use 

 of hydrocyanic acid gas for this work. This has 

 been used for a number of years in fumigating 

 plants in the open air, but it is only recently that 

 it has come into general use for greenhouse pur- 

 poses. Through the efforts of Messrs. Albert F. 

 Woods and P. H. Dorsett, who have been associ- 

 ated with the writer in work on plants under glass, 

 experiments were inaugurated several years ago 

 to test the value of this gas in the greenhouse. 

 At this time we were having serious difficulty 

 with our violets from the attacks of aphides, and 

 it was a question as to whether it would not be 

 necessary to either give up growing the crop or 

 adopt some method of getting rid of the pest 

 other than those usually followed. After many 

 experiments it was found that the gas could be 



