200 AGRICULTURE 



or brown. Instead of seeds, they produce spores, minute bodies 

 which bud or break off from the fungi. These reproduce with 

 wonderful rapidity. One plant may produce several millions 

 within twenty-four hours. Spores are so small and light that 

 they are borne far and wide in the air. 



Some fungi perish under unfavorable conditions. Others es- 

 tablish a colony on a host, as the plant or animal on which they 

 fasten themselves is called. A very unwilling host it is, we may 

 be sure, which is deprived by its guest of tissue or juices or even of 

 life. The fungi penetrate the cell walls of their host, devour the 

 protoplasm which, as you have learned, is the living principle; 

 they destroy cell after cell, and weaken or kill the host plant. 



Bacteria are so small that they have to be magnified before we 

 can perceive them at. all. Under the microscope, they are seen 

 to have one of three forms ; they are ' shaped like balls, pencils, 

 or corkscrews.' 



You have learned that some bacteria help the farmer by chang- 

 ing nitrogen into forms which plants can use, and others harm him 

 by consuming soil nitrogen. There are other fungi which harm 

 him by feeding on his crop plants, producing such diseases as 

 rot, rust, smut, mildew, blight, scab, and wilt. 



It is important for the farmer to learn something about fungi. 

 He is then better able to get the aid of the helpful ones and to 

 check the 'ravages of the harmful ones. 



Fire Blight. The bacteria which cause fire blight of fruit trees 

 are carried by insects at blossoming time. Thus they spread from 

 tree to tree, from neighborhood to neighborhood. The bacteria, 

 use the food prepared in the leaves for the tree, and kill leaves, 

 twigs, branches, often the tree itself. The disease is called fire 

 blight because the leaves affected look as if they had been scorched 

 by fire. 



