284 GENERAL BOTANY 



of bacteria and their poisonous toxins by means of the blood 

 stream in animals. As a consequence, the period of disease 

 production is greatly prolonged in plants as compared with 

 animals, and may continue in perennials, like trees, for many 

 years without causing death. 



The exact manner in which fungi destroy plant structures and 

 materials which are commercially important to man varies with 

 the fungus and the host. In the case of forest trees the damage 

 comes from the breaking down of the tissues of the tree, so that 

 the wood is injured, as well as from the checking of the healthy 

 growth and development of the tree. In herbaceous plants the 

 fungous disease usually weakens the plant to such an extent 

 that its productiveness is greatly lessened, or it may destroy 

 the plant entirely. In other cases, as in the attack of grain by 

 smuts, the spores are formed in such numbers in the ovules 

 that the grain itself is almost entirely destroyed. In soft plant 

 structures, like fruits and potatoes, the mold or other parasite 

 simply starts the process of decay, which is then carried on by 

 bacteria until the entire structure is destroyed. 



Remedies. The remedy for the great losses in food, lumber, 

 and nursery stock, which result from fungous diseases, lies in a 

 better knowledge of the nature of these diseases and in a more 

 strict oversight, on the part of individuals and of state and 

 national governments, of their control and dissemination. The 

 United States government now employs expert plant pathologists, 

 who study the origin and spread of plant diseases throughout 

 the country. They are also cooperating with state governments, 

 through the state experiment stations, in an endeavor to check 

 the progress of dangerous fungous pests. Expert pathologists 

 are also maintained by the United States government to inspect 

 imported seeds and plants, so as to prevent the introduction of 

 plant diseases from foreign countries. Entire shipments of fruits, 

 vegetables, and nursery stock are often condemned by these 

 government officials and denied entrance into our ports. Much 

 insight is also being gained into the various methods of control- 

 ling various diseases by sterilizing seeds before planting and by 

 the destruction of certain fungous hosts which harbor dangerous 



