282 GENERAL BOTANY 



The dissemination of fungi by spores lodged on seeds or by 

 means of mycelium within the seeds is another method of spread- 

 ing fungous diseases. The rusts and smuts are often thus dis- 

 seminated by spores lodged on the kernels of the grain when the 

 seeds are sown. These spores then germinate with the seeds and 

 attack the young seedlings while their tissues are tender and 

 allow the fungus hyphse to penetrate them. 



Beans are infested with a fungous disease known as anthracnose, 

 which often does great damage to the crop. The mycelium of the 

 fungus causing the disease grows into the ovule during its active 

 vegetative life and hibernates there during the resting period of 

 the seed. The next spring, when the beans are planted, these 

 hibernating hyphse also grow and form a mycelium throughout 

 the tissues of the bean plant. If conditions are right for vigo- 

 rous fungus growth, the mycelium attacks the pods and develop- 

 ing seeds and destroys the crop. 



In this manner a dangerous disease may readily be spread 

 through the exchange or sale of seed, and the infection of a pre- 

 vious year may cause the real damage to the crop in the year 

 following infection. Local spreading of fungous diseases is often 

 caused in forests by certain fungi which attack the roots of trees. 

 These fungi form long stolons, composed of fungus hyphse, 

 which grow for considerable distances and penetrate the roots of 

 adjacent trees, infecting them with the disease. 



In addition, dissemination of fungi is effected by water, as 

 in the water molds (Saprolegnici), .by animals (including insects 

 and fish), and by man in the shipping and transportation of plants 

 and plant parts from state to state and from one country to 

 another. The spread of disease by this method has been greatly 

 increased in recent years by the shipping of seeds and entire 

 plants from state to state and from European countries into 

 the United States. 



Infection. Plants have few openings into the inner tissues 

 of the body, corresponding to the nose, mouth, and ears of man 

 and other animals, through which germs can enter and cause 

 disease. Infection in plants, therefore, is more likely to take 

 place through wounds or through the stomata. 



