502 ANNUAL REPORT OF THE Off. Doc. 



2. Internal fungi — downy mildew of grape, scab, fruit rots, canker, 

 etc. — whicli continue tlieir develoijment wholly within the 

 tissues of the parts attacked and which are thus prevented 

 from developing only by destroying the germinating tube of 

 the fungus before it penetrates the skin. (Fig. 2.) 



Physical Pkoperties of Mixtures. 



Ill order to know just how to use and apply the different spraying 

 liquids now in common use, it is necessary to understand and appre- 

 ciate their physical properties, their behavior in the tanks, in the 

 pump, at the nozzles and on the plants. To do this most conveniently, 

 spray mixtures may be divided, irrespective of their insecticidal or 

 fungicidal properties, into three general classes: 



1. Mixtures involving the suspension of insoluble substances Id 



water; for example, Paris green and other arsenites, Bor- 

 deaux mixture. 



2. Mixtures consisting of simple solutions; for example, copper 



sulphate solution, ammouiacal copper carbonate, sulphide of 

 potash, different soap solutions, solutions of lye or caustic 

 soda. 



3. Emulsions or mechanical mixtures of oily or waxy substances 



with water; for example, kerosene and crude oil emulsions, 

 or the kerosene and crude oil mixtures v/ith water through 

 the medium of the pump and nozzle, without the aid of emul- 

 sifying agents. 



Mixtures Consisting of Insoluble Materials in Suspension. 



In the mixtures of this first class, insoluble substances are to be 

 suspended in water and applied while in suspension. It is import- 

 ant to bear this in mind, as upon this fact depends not only the 

 method of application but also the method of maintaining the com- 

 pound on the fruit or leaves, as the case may be. It is necessary' that 

 tlie mixing be thorough in order that the material may be equally 

 disseminated throughout the liquid. For unless it is, the distribu- 

 tion of the poison or fungicide will not be uniform, and hence effec- 

 tive results cannot be obtained. The insoluble material is kept in 

 suspension by means of agitating the liquid either by a separate 

 agitator or by a devise attached to the pump handle. 



Agitators Considered. 



Ihe proper and thorough agitation of sprays of this class is one 

 of the most important points in the successful use of the materials 



