64 HATCH EXPERIMENT STATION. [Jan. 



upon dead and decaying organic matter. These are entirely 

 harmless to plant life. Still others, while ordinarily sapro- 

 phytes, have parasitic tendencies, and may attack plants in a 

 weak and unhealthy condition. A sickly or injured plant 

 may be attacked by a variety of such forms, together with 

 true parasites, bacteria, insects and other organisms both of 

 the animal and vegetable kingdoms, making it impossible to 

 say which waa the original cause of the trouble, if, indeed, 

 any one of them could be strictly considered as such. 



A leaf spot produced by fungi is a place on the leaf where 

 a fungous plant has become established and consumed the 

 vital substance. The spot becomes larger as the fungus 

 grows out into new tissue. Fungi reproduce themselves by 

 spores, corresponding to the seeds of higher plants. These 

 spores are of course extremely minute, and are produced in 

 infinite numbers. They are smaller than the finest dust, and 

 float about in the air with the greatest readiness. 



In the treatment of fungous diseases only one course of 

 action can be successful. This is prevention. A leaf once 

 infested with a fungus can never be restored to its normal 

 condition, for not only is the fungus within its tissues and 

 out of reach of any treatment, but, furthermore, certain parts 

 of the leaf are already dead, and can never be restored. One 

 method of preventing such diseases is by killing the spores 

 before they can germinate. The now common operation of 

 spraying consists in applying to plants affected or liable to 

 be affected by disease certain substances diluted with water 

 to a strength sufficient to destroy the fungous spores but not 

 injure the leaves. This solution is applied in the form of a 

 fine spray, by means of a pump and nozzle. The application 

 of this method is now well established in the treatment of 

 most of our destructive plant diseases, especially those affect- 

 ing fruits and vegetables. The most eflTective substance thus 

 far discovered for spraying purposes is the so-called Bor- 

 deaux mixture, — a sort of blue whitewash, made by com- 

 bining lime with copper sulphate (blue stone, blue vitriol). 

 Many other substances have been tried, some with great 

 success ; but the Bordeaux mixture is still the most satis- 

 factory for general purposes, for it kills the spores, sticks 

 to the leaves and does not injure the plant. 



