FUNGICIDES AND THEIR APPLICATION 99 



practically confined to sulphur, to mixtures of sulphur and lime, 

 and of sulphur with 10 per cent, of dry arsenate of lead. Recently 

 dry Bordeaux powders have been placed on the market and 

 are coming into favour, but it is difficult to foresee a future 

 for them in places liable to tropical showers. There are various 

 types of dusting machine to be obtained, the best of which, 

 short of power or traction outfits, are certain types with hand- 

 operated fans. For garden purposes sulphur may be sifted out 

 from a cotton bag. 

 Disinfectants. 



The principal use of disinfectants in plant pathology is for 

 the treatment of seeds ; they also have an application to certain 

 other forms of planting material, to the stems and branches of 

 trees, to wounds and, to a very limited extent, to the soil. 

 Disinfection of Seed. 



In a number of diseases the disinfection of seed affords the 

 best opportunity of eliminating a parasitic organism or of reducing 

 its prevalence in the resulting crop. It is of particular value 

 with new introductions, and in planting short-term crops after 

 rotation or a close season. 



As a general rule disinfection only extends to spores or other 

 material adhering externally, but in the case of certain smuts 

 it is possible to destroy internal mycelium bj^ means of heat. 



There is no universally applicable method of seed dis- 

 infection. There are such marked differences in the suscepti- 

 bility to poisons of seeds on the one hand and parasites on the 

 other that a treatment which is successful in one case may 

 entirely fail in another. There are spores, for example, which 

 can germinate in strong Bordeaux mixture and others which 

 can withstand immersion for a considerable time in i per cent, 

 copper sulphate solution. Difficulties are experienced in securing 

 the wetting of certain kinds of seeds, as for example cotton seed, 

 which is difficult to free from the air entangled in the fuzz. 



Corrosive Sublimate. 



Mercuric chloride, or corrosive sublimate, has a wide range of 

 effectiveness. It is used in solution in water, most usually at a 

 strength of one part in a thousand (i oz. to 6 J gallons). It has 

 been used on a considerable scale for soaking cotton seed, but the 

 method is subject to the disability mentioned above unless the 

 seed has been delinted with sulphuric acid or wetted with alcohol, 

 measures only applicable on a small scale. The effects of 

 mercuric chloride are liable to be neutralized by the presence of 

 organic substances of an albuminous nature, and it is inad- 

 visable to use the same lot of solution more than once. It is 

 desirable to wash seeds after treatment. 



The solution is often recommended for use as a disinfectant 

 on newly exposed wood of trees, preparatory to a more per- 

 manent coating of a preservative paint. 



