220 THE PRINCIPLES OF FLORICULTURE 



foliage when it is coated with the salt crystals ; and after one or 

 two thorough applications of the solution, comparatively few of 

 the insects will be found." 



264. Effects of sulfur. Fumes of sulfur succeed in keeping 

 the red-spider in check, but destroy only a few. About one- 

 quarter of a pint of sulfur is mixed thoroughly with one quart of 

 boiled linseed oil, and this mixture is painted on the pipes. 



255. Pests exterminated by tobacco fumes. Different forms 

 of tobacco preparations are used to keep the sucking insects 

 in check. These preparations are especially effective with the 

 various forms of aphis, but less so with scale insects, white fly 

 and thrips. They cause suffocation by closing the breathing 

 pores of insects. 



256. Tobacco products most used. In the earlier days of 

 fumigation, tobacco stems and other waste tobacco products 

 were generally used. They were usually burned, filling the house 

 with smoke. They were effective in their destruction of many 

 insects, but left disagreeable odors in the houses, and more es- 

 pecially were they detrimental to the fragrance of many flowers. 

 Recently, various extracts of tobacco have come into popular 

 favor, among these being " Aphicide," " 40 per cent Nicotine," 

 " Nicotiana," " Aphine," " Nicoticide " and " Nicofume." 

 These preparations are considered by many to be expensive, 

 but their effective destruction of insects, and the small quantity 

 necessary, bring them within the means of most florists. These 

 extracts rarely leave disagreeable odors on the flowers. 



257. Pests exterminated by tobacco dust in the soil. 

 Asters are frequently attacked by a blue aphis which sucks the 

 juices from the roots. If a small handful of tobacco dust be 

 placed about the roots of the plants when they are set in the field, 

 these insects will be kept in check. 



258. Pests exterminated by poisonous fumes. Most green- 

 house pests may be destroyed by fumigation with hydrocyanic 

 acid gas. As the nature of this is now better understood, it is 

 coming into general use. White flies, mealy bugs, and soft and 

 hard scale insects are among those killed by this treatment. 



259. Effects of gases on insect and plant life. Insects must 

 breathe, and so long as gases penetrate everywhere, the solution 

 of the problem of insect extermination by poisonous gases seems 

 to lie in the use of such gases. Unfortunately, these gases may 

 also be injurious to plant life. The problem of the fumigator, 

 therefore, is to liberate sufficient poisonous gas in a house to 

 kill all insects without injuring the plants. 



To determine the correct amount, requires careful study and 



