52 MAINE AGRICULTURAL EXPERIMENT STATION. 



that must be met, each in a different way. These enemies may 

 be grouped first under the two general heads, — insects and 

 fungi. 



The insect enemies are naturally divided into distinct classes 

 which must be met in very different ways, and the same is true 

 of the fungi. The first class of insect enemies includes those 

 that, either in the mature form or as larvae, eat the plant tissue ; 

 e. g., the plum curculio, the codling moth, the currant worm, 

 the tent-caterpillar, the potato beetle, etc. These are very 

 readily destroyed by the application of some form of arsenic, as 

 Paris green, to the parts which will be eaten. 



Another class of insects, e. g., the plant lice and some of the 

 scale insects, obtain their food by sucking the juices of the plant 

 and, therefore, are not affected by an application of poison. 

 These must be overcome by an external irritant, such as kero- 

 sene, or an alkali like caustic soda or strong soap suds, or by 

 some material that will close the breathing pores and thus stop 

 respiration, e. g., pyrethrum or hellebore (in the dry form helle- 

 bore acts in both ways.) 



Fungi (singular, fungus) are simply low forms of plant life 

 which feed upon organic matter, either living or dead. Those 

 which grow on living tissues — parasitic fungi — are the ones with 

 which we are specially concerned. It is these which cause many 

 of the blights and rusts, and smuts and scabs and mildews of 

 various plants. Fungi are propagated by means of minute, 

 microscopic bodies, called spores, which are carried from place 

 to place by the wind and by insects, birds and other animals. 

 A spore, falling upon the surface of a leaf, or the growing tip 

 of a branch, if in the presence of moisture and the usual summer 

 temperature, germinates in a manner very similar to that of a 

 seed. If the surface of the leaf or fruit is coated with some 

 material which is destructive to the young fungus, as the spore 

 germinates, all the damage from the parasite is warded oft". If, 

 on the other hand, there is even a small spot that is not coated, 

 there is opportunity for the parasite to obtain a foothold. With 

 few exceptions, after the parasite has once attacked the plant, 

 spraying is of little if any avail. 



