212 



CIVIC BIOLOGY 



(the host is the organism that supports a parasite), in 

 which he lists 174 plants, with the fungi that attack each. 

 From this we see that everything we try to raise has its 

 fungus enemies : alfalfa has anthracnose, leaf spot, root gall, 

 European root disease, and root rot ; the apple has 24, among 

 them anthracnose, or bitter rot, fire blight, crown gall, rust, 



and scab ; beans have 7 ; 

 corn, 6 ; cotton, 9 ; the 

 grape, 9 ; potato, 6 ; 

 tomato, 8 ; wheat, 7 ; 

 violet, 6 ; pine, 6 ; oak, 

 7; and so on through 

 the list. 



The following bacte- 

 rial diseases are common : 

 Pear and apple blight. 

 Leaves turn brown as 

 though burned with fire. 

 The germ was supposed 



FIG. 101. Loose smut of oats (Ustilago 

 avence) and normal heads 



to be carried by bees to 

 the blossoms, but it is 

 probably inoculated by 

 aphides. Limbs that show symptoms of the disease should 

 be cut below traces of the blight and burned. 



Wilt disease. This disease affects tomatoes, cucumbers, 

 melons, cotton, and Irish potatoes, and causes the plants to 

 wilt rapidly and die. 



Black rot of cabbage. The germ attacks cabbage, turnips, 

 rutabaga, and .cauliflower. Leaves turn black and the plant 

 dies. This disease is common in America and Europe. 



Try, at least, to make a preliminary survey, and then 

 choose for intensive study the local types that are most im- 

 portant, and especially those that require general knowledge 

 and united effort of the community to control the civic 



