AGRICULTURE. 



CHAPTER XVIII. 



THE DISEASES OF PLANTS. 



EFFECTS OF DISEASE. House plants, especially those with 

 large leaves, often become covered with small dark spots which 

 gradually become larger and make holes in the leaves, which 

 soon die. We can see the same on the leaves of the apple tree, 

 the pear tree, and can also find them on the leaves of the shade 

 trees. This spotting of the leaves is a disease. We can find 

 similar diseases on the leaves and stalks of grain. 



When plants become diseased, they lose some of their 

 vitality, as we say, and we need not look for much fruit or 

 grain. It is therefore of importance that disease among plants 

 be prevented, just as we try to prevent sickness of animals, 

 or of ourselves. 



Again, in addition to the disease attacking the leaf, the 

 branch, the stalk, or the root, it may attack the fruit. You 

 have seen the brown and black spots or scabs on the apple and 

 the pear ; you have seen the ear of corn all overgrown with smut, 

 and the heads of wheat and other grains covered with a dirty 

 growth ; you have seen the potatoes affected by the "scab" 

 and the " rot." All of these are cases of disease. Whenever 

 the plant is diseased in any part the fruit or the seed 

 will be found to be either small and of a poor shape or 

 else entirely useless. Scabby apples, smutty corn, and 

 potatoes affected with the "rot" are not salable, they are of no 

 use, in fact they are harmful. Why are they harmful ? In the 

 first place, such food is not wholesome. Further, we know 

 that very often one animal will take disease from another 

 scarlet fever, diphtheria, small-pox, and even influenza, ora "cold" 



