THE DISEASES OF PLANTS 



99 



sulphur ; to make this solution, use one ounce of the liver 

 of sulphur to two gallons of water. 



The fungus that causes the pear leaf spots has its 

 spores in little pits (Fig. 85). The spores of some fungi 

 also grow on stalks, as in Fig. 86. This figure repre- 

 sents an enlarged view of the pear scab, which causes so 

 much destruction. 



You see, then, that fungi are living plants that grow 

 at the expense of other plants and cause disease. Now 



FIG. 86 



The spores of the pear scab fungus are borne on stalks 



if you can cover the leaf with a poison that will kill the 

 spore when it comes, you can prevent the disease. One 

 such poison is the Bordeaux Mixture (pronounced bor-do^\ 

 which has proved of great value to farmers. 



Since the fungus in most cases lives within the leaves, 

 the poison on the outside does no good after the fungus is 

 established. The treatment can be used only to prevent 

 attack, not to cure, except in the case of a few mildews that 

 live upon the outside of the leaf, as does the rose mildew. 



