XII 



THE PRINCIPAL DISEASES 



There are many diseases which attack the apple 

 tree or fruit, but as far as the practical business of 

 fig-hting them is concerned only three or four need be 

 seriously considered. The most destructive of these 

 are caused by fungi. These fungi are very small 

 plants, usually so small that a high-power microscope 

 is required to see them. However, they make up in 

 numbers for what they lack in size. They are parasites, 

 living on the apple tree, foliage or fruit, and taking 

 the nourishment which the fruit grower never in- 

 tended for them. 



These fungi are usually distributed by means of 

 spores, which take the place of seeds, but are thousands 

 of times smaller than even the proverbial mustard seed. 

 These spores are usually carried by the wind, and they 

 usually lodge in the rough bark or on the rough bud 

 scales of the apple trees. They can be killed most easily 

 just at the moment when they germinate, and the best 

 thing for killing them is some form of copper solution. 

 Here is where the copper sulphate of bordeaux mixture 

 comes in. As soon as the spores germinate the fungous 

 plant which grows from them penetrates into the tis- 

 sues of the apple bud, twig or leaf, and is then quite 

 out of reach of any remedy. 



While every disease has its own specific fungu'S and 

 behaves in its own peculiar way, this general statement 

 fairly covers the case for all our common fungous dis- 

 eases. A brief consideration of the facts here recited 



