46 



violets were planted September 15, and. though given the best of care- 

 ful attention as to air, light, and water, our correspondent succeeded 

 in obtaining nothing but "green" violets. 



LITEKATURE. 



In addition to the technical paper b} T Mr. Pergande previously noted, 

 several notes and extracts from correspondence have made their 

 appearance in different florists' journals during the past two years in 

 which the species has been studied from the practical side. It has 

 also received consideration in Mr. Galloway's "Commercial Violet 

 Culture,'' where it is discussed with the so-called green aphis, on pages 

 198-208. The chapter referred to is devoted principally to the use of 

 the hydrocyanic-acid gas method of treatment for these aphides and 

 has less to do with their biology, although the nature of injury is 

 described somewhat in detail. 



In the Transactions of the Roval Society of Canada (Vol. V, second 

 series, 1899-1900, p. 228), Dr. James Fletcher states that this pest had 

 caused much damage to violets during u the past winter." and that it 

 had made its first appearance in Canada about 1897; and, in his "Re- 

 port of the Entomologist and Botanist for 1899" (19ow pp. 177-178), 

 he has given an account of injury in a large florist's establishment in 

 Toronto. The loss was estimated at $1,000. Reference to the same 

 matter is given in the Report of the Entomological Society of Ontario 

 for 1S99 (1900, p. 110). 



Prof. W. G. Johnson briefly noted injury to violets in Maryland 

 during the season of 1900 (Bui. 26. new series, p. 81); also in the 

 American Agriculturist for December 29, 1900, and elsewhere he has 

 furnished some notes on the treatment of a greenhouse in Maryland 

 affected by this plant-louse. One of the owners in this case stated 

 that a single demonstration of this method was worth to him at least 

 $250 that season. 



[REMEDIES. 



Hydrocyanic-acid gas alone is a sufficient remedy for this species. 

 A spray of neutral soap or of water will also kill the insect. These 

 remedies are treated in previous pages. Concerning the gas treat- 

 ment, it should be said that it is due to the ravages of this plant-louse 

 in the vicinity of the District of Columbia more than to anything else, 

 perhaps, that the hydrocyanic-acid gas method of treatment was 

 brought to its present state of perfection as a method of controlling 

 insects infesting plants grown under glass. Until the adoption of this 

 means of fumigation, tobacco, which has been in use as a greenhouse 

 insecticide, or. more properly speaking, repellent, for upward of a 

 century, was the remedy most relied upon. The danger of using 

 tobacco in violet greenhouses is treated somewhat at length in an arti- 



