500 ANNUAL REPORT OF THE Off. Doc. 



Poison sprays, such as Paris green, arsenite of copper, arsenite of 

 lime, arsenate and arsenite of lead, and arsenical poisons generally. 

 These are effective against the first class of insects only. 



Contact sprays^ such as kerosene, crude petroleum, the lime, salt 

 and sulphur wash, whale oil soap, rosin wash, pyrethrum, and to- 

 bacco. These kill the insects by their caustic action or by closing 

 up his breathing pores and thus suffocating him. The second class 

 of insects can be destroyed only by these. Insects of the first class 

 may also be destroyed by contact sprays, but only in rare cases 

 is this class of mixtures so employed. 



Fungi. 



In order to understand fully the action of remedies against the 

 other class of enemies which the fruit-grower has to combat, the 

 fungi, it will be well to consider somewhat in detail the definition of a 

 fungus — just what it is, how it lives and grows. 



What is a JFungusf — A fungus is first of all a plant. It belongs 

 to a lower order of plants, differing essentially from the more 

 familiar "higher" plants in possessing no chlorophyl, or green color- 

 ing matter. It is incapable of assimilating inorganic (mineral) sub- 

 stances, and is therefore dejjendent upon organic matter either liv- 

 ing or dead, upon which it grows and derives its sustenance just 

 as the higher plants derive theirs from the soil. It has uo leaves, 

 bat it has something akin to roots and stems, the mycelium, and its 

 means of reproduction and spread, the spores, analogous to the seeds 

 of higher plants. The spores are perhaps the most important part 

 of the fungus from the point of view of the fruit-grower, for it is by 

 the means of these that the disease or destruction by the fungus is 

 spread from leaf to leaf, from fruit to fruit, or from tree to tree. 

 Any agency, then, which may disseminate the spores may be the 

 means of spreading the disease caused by the fungus. Wind, rain, 

 insects, birds, animals and even man himself are known to act in 

 this capacity. 



Hoio a Fungus Grows. — Now, what takes the place when one of the 

 spores falls or is placed upon a leaf or a fruit? If the conditions of 

 temperature and moisture are favorable it will germinate — just 

 as a seed does when planted in moist, warm earth — and send 

 out a small tube, known as the "germinating tube" of the fun- 

 gus. These spores with their germinating tubes are exceedingly 

 small and can be seen only with a compound microscope. Plates 

 II {a) and II {h) are reproduced photo-micrographs of bitter rot 

 spores before and during germination, all greatly enlarged. From 

 this point fungi differ in their development, in the manner 

 in which they grow and extract their nourishment from the 

 parts of the host plant attacked. In one class the germinating tube 



