CHAPTER XXIX 
SOME GENERAL PLANT PROBLEMS 
Students of botany had to make a study of plants before 
they could understand how to keep plants well, how to 
produce new kinds of plants, and how to solve similar prob¬ 
lems. It is more important to-day than ever before that 
such problems be solved simply because there are more human 
beings living to-day than at any previous time. In the pre¬ 
ceding chapters on parts of plants, you have been making a 
scientific study which has furnished you with reliable facts 
about the life of plants. This is the kind of study that all 
who know about the life of plants have made, and it should 
make it easier for you to understand the few general plant 
problems which have been merely outlined in this chapter, 
because whole books are needed for a complete discussion 
of them. 
317. Plant Diseases. — Three typical plant diseases', Cab¬ 
bage Yellows, Potato Wart, and Black Stem Rust, have been 
selected to illustrate how some of the fungi destroy our 
food plants. As you learn about each of these diseases, you 
will see that it is much more important that the disease be 
prevented than cured. Note the kind of knowledge neces¬ 
sary to recognize them and the methods used in treating 
them. In the case of the rust your attention is called to 
the complicated life history of this fungus parasite as it lives 
first on the wheat, then on the wild barberry in a never 
ending cycle. 
The farmer who would be successful must learn, how to 
recognize the common diseases of farm plants. If he does 
not know about this important part of farming, he can ask 
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