PLANT DISEASES. 243 



ter season, and may be called winter spores. The my- 

 celium is ready to form a crop of summer spores within 

 a few days, or at most a few weeks from the beginning 

 of its growth, and usually spores are produced more 

 or less continuously by the fungus plant during its life. 

 Seasonal and weather conditions influence the ger- 

 mination of spores and the growth of fungi, more even 

 than they influence the growth of higher plants. These, 

 along with other conditions, cause diseases due to fungi 

 to be more prevalent in some seasons and in some lo- 

 calities than in others. 



EXERCISE. Are seeds and spores similar? If not, state the dif- 

 ference in their structure. Bring some toadstools, puffballs and 

 molds to school and examine their structure. Do they correspond 

 to the description given of them in this article? 



SECTION XXXVI. CONTROL OF FUNGUS DISEASES. 



A diseased plant can seldom be cured; but in most 

 cases it is possible to prevent the spread of the disease 

 to sound parts of the affected plant or to other plants. 

 The fungus must be given the least possible chance for 

 its spread and growth; and at the same time the crop 

 must be given the best chance for strong and vigorous 

 growth. 



Means of Control. The exact means of control 

 will vary with the crop and the disease, and are best 

 considered in the accounts of diseases which follow. 

 Here may be mentioned proper cultural methods that 

 will produce a vigorous crop, resistant to contagious 

 as well as functional diseases; rotation of crops that 

 will lessen or eradicate diseases by eliminating their 

 host plants, except at intervals; the cleaning up and de- 

 stroying of all crop remains at the end of the season, 

 thus lessening the chances for the fungus to survive the 

 winter; destruction of volunteer plants and weeds along 

 fences and roads, to control those diseases common 

 to those and to crop plants, as well as other diseases 



