PLANT DISEASES 243 



Potassium sulphide solution. The potassium sulphide solu- 

 tion is made by mixing one ounce of liver of sulphur with 

 three gallons of water. It is used as soon as made, and is an 

 excellent remedy for mildews. 



Preventive measures. Since few plant diseases can be com- 

 pletely cured and many are only held in check with difficulty, 

 it is wise to take every precaution against the entry of dis- 

 ease. Some plants are more resistant than others of the same 

 species, and these should be grown. In some cases it seems 

 possible to breed up a resistant strain. Disease always attacks 

 the less thrifty individuals first. Plants should be kept in 

 good health by proper cultivation and thus rendered more 

 resistant. Diseased plants, when they occur, should be removed 

 and burned. If allowed to remain, they only spread the trouble 

 to other healthy individuals. Burning the plants kills the 

 spores that might otherwise set up new areas of infection. 



PRACTICAL EXERCISES 



1. List the plant diseases known to be in your locality. Underscore 

 the most destructive. 



2. Tear apart decaying logs and examine the white threadlike 

 growths which form the plant body of the higher fungi. See if you 

 can trace the fruiting parts of puffballs, mushrooms, and shelf fungi 

 to such plant bodies. 



3. Examine the "smoke" from a puffball with microscope. The 

 small objects seen are spores. Draw several. 



4. Make a spore print by placing the cap or top of a mushroom, 

 with gills down, upon a piece of clean paper. Cover with a bell jar or 

 drinking glass for a day. The spores will be discharged in immense 

 quantities. Some species have white spores, and these will show best if 

 colored paper is used. 



5. Make a collection of leaves and stems to show rusts, mildews, 

 leaf spots, and smuts. These should be preserved, with proper labels, for 

 the use of other classes. 



6. Scrape off some spores from specimens affected with rust and 

 examine with the microscope. The summer spores are one celled, but 

 the winter spores are usually two or several celled. 



