194 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



treated by causing them to leap or fly against a " hopper doser " 

 of some form. A hopper doser consists of a surface of tin, or 

 other material, covered with printer's ink, tar, or some other 

 sticky substance, which holds the insects captive that touch it. 



Defoliating Insects. — The insects eating the leaves of plants 

 are, as a rule, the easiest insects to destroy, and at the least 

 expense, because the leaves maybe covered with relatively cheap 

 poisonous substances ; and as the insects eat the leaf they will 

 also consume the poison, and thus end their existence. Only 

 the more valuable field crops can be treated economically, how- 

 ever, for even as cheap a process as this is too expensive for 

 most of the staple crops. Insects of the defoliating class can 

 also be killed by the same remedies used for sap-sucking forms ; 

 but with those remedies, as is true of the insects of the former 

 class, the insect must actually be touched by the remedy to be 

 affected by it. 



Fungi. 



External Fungi. — One can easily, with the aid of a small 

 microscope, see the threads of the fungus. All parts of the 

 plant above ground are affected, but the young leaves and the 

 ends of stems are most readily attacked. They may be 

 destroyed, and the spread of the fungus stopped, by the use of 

 the vapour of sulphur. 



Local Fungi. — Most of the rusts and spot fungi may be 

 classed under this head. They live within the plant, and 

 so cannot be destroyed after they once gain an entrance. A 

 cure, therefore, is impossible, and attention must be turned to 

 preventing their entrance. The spores are produced very 

 abundantly and quickly in most species, so that, if treatment is 

 not given soon after the first appearance of the trouble, it will 

 be seen to spread with great rapidity, and involve a much larger 

 part of the plant. The theory of treatment is to keep the 

 plant covered with some substance which will prevent the 

 germination or sprouting of the spores, thus preventing the 

 fungus from entering a new part of the plant. We now know 

 a number of very effectual substances which will produce this 

 result. 



Penetrating Fungi, — This is the most difficult group of fungi 

 we have to deal with. Grain smuts, blackberry rust, and curl- 

 leaf of the peach are examples. In annual plants the infection 



