CHAPTER XV 

 INSECTICIDES, FUNGICIDES, ETC. 



ANY detailed account of those investigations on the nature of 

 certain insecticides and fungicides which have been undertaken 

 at Woburn, would be somewhat out of place in the present 

 work, and those who wish to inquire into the matter should 

 refer to the original communications dealing with these subjects. 

 The number of substances investigated, however, has not been 

 large, and to supply a more general view of the subject, a 

 quotation may be made, with the publishers' permission, from 

 an article on plant-sprays, written by one of the present authors, 

 for Sir E. Thorpe's Dictionary of Applied Chemistry. 



PLANT-SPRAYS 



Spraying may be taken in a wide sense to embrace the applica- 

 tion of solids, liquids or gases to plants, with the object of freeing 

 them from insect or fungoid pests, or of cleansing them from dead 

 bark, and such adventitious deposit or growth as interferes with 

 the healthy functions of the plant. 



Solids 



Many liquid spray-fluids, or washes, contain solids in sus- 

 pension, but it is only in a few v cases that solids are used in the 

 dry state ; in such cases they are blown on to the plants by 

 means of bellows, and the operation must be performed while 

 the plants are wet with dew or mist, so that the solid may adhere 

 to them. 



Sulphur, in the form of flowers of sulphur, is applied extensively 

 in this way to hops for destroying mildew and red spider, and in 

 certain other cases it is applied mixed with lime. The nature 

 of its action is at present obscure, but most probably depends 

 on its being slightly volatile, for, when used in hot-houses, the 

 most satisfactory results are obtained when it is painted on to 

 the hot-water pipes, or otherwise heated. At the same time its 

 effectiveness is increased by the presence of moisture, though it 

 hardly seems possible that the traces of sulphuric acid formed 

 under such conditions can account for its action. 

 L M5 



