52 



JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



and burning it or by burning dried Tobacco leaf, which is practically the 

 same thing. 



The first and second methods of using nicotine are reasonable and 

 scientific, and are strongly recommended to give satisfactory results. The 

 third method is clumsy, unreliable, and by no means unlikely to cause 

 injury to plant life. But I will take the three methods seriatim and 

 explain the working of each. 



The first and principal method, by the application of heat to nicotine 

 (but not by direct flame) and by bringing the vapour so produced into 

 contact with the plant or plants requiring treatment. In using this 

 method it is necessary that the two following facts should be borne in 

 mind, viz. first, that nicotine has a very high boiling point, 250° C. ; and 

 secondly, that the less heat we apply to nicotine to vaporise it, the more 

 potent as an insecticide will the resulting vapour be. It is further essential 

 that the vapour should be given off rapidly, so that even a small amount 

 of heat should not be applied to the nicotine for a longer time than is 

 absolutely necessary. 



All these points are met by mixing nicotine with a volatile substance 

 which prevents the temperature from rising too quickly when heat is 

 applied, and also causes the nicotine to be rapidly vaporised, the vapour 

 of the substance with a low boiling point carrying with it mechanically 

 the greater portion of the nicotine with which it has been mixed. If the 

 vaporisation of nicotine is carried out in this manner, then good and 

 lasting results (and no damage) will accrue to plant life. Nicotine can 

 be procured ready mixed with volatile matter in the proper proportions, 

 and is sold under the name of fumigating compound. The amount of 

 the compound required to fumigate 1,000 cubic feet is half an ounce. 



The above method of using nicotine is the one usually adopted when 

 it is required to cleanse all plant life in a hot or cold house, but some- 

 times there are individual cases in a house requiring treatment. Yet it 

 would be waste of time and money to fumigate the whole house. This 

 is where nicotine is applied under method No. 2, viz. by direct appli- 

 cation to the plant in a liquid form. 



When it is required to apply nicotine directly to the plant, it is 

 usually mixed with other substances that cause it to adhere to the leaves, 

 and the mixture is then diluted with water. A syringe with a fine nozzle 

 is used, or, better still, a spraying apparatus, which causes the liquid to 

 be more evenly distributed, and thus prevents waste of material. Nico- 

 tine so used brightens the foliage, does not stain, and will not injure the 

 roots or retard the growth of the plant so treated. 



The third method of using nicotine by mixing it with combustible 

 fibrous material, or by using dry Tobacco leaf and burning the mass, is, 

 as 1 said, clumsy, unreliable, and likely to cause injury to the plants so 

 treated. Nicotine is destroyed if brought into direct contact with 

 flame. 



In the combustion of nicotine another compound, pyridine, is formed, 

 which is distinctly injurious to plant life. People who indulge in exces- 

 sive smoking arc; not injured by the nicotine in the tobacco used, but by 

 the pyridine formed in the burning Tobacco. . . . 



The method of fumigating by burning Tobacco paper or rags, or 



