PLANT DISEASES 185 
when it has become diseased. Mildew, potato blight, and 
leaf spot are some of the common diseases for which we 
spray, and Bordeaux mixture, which is made from lime and 
copper sulphate, is the principal remedy employed for the 
purpose. 
Disease-resisting Seed.— We know that some persons 
“catch ” contagious diseases more quickly than others do. 
It is the same with plants — some of them become infected 
with a disease while others standing quite near them resist 
the attack. Scientists have therefore been trying to secure 
strains of disease-resisting seeds. The process is very simple, 
and any intelligent person can easily understand it. We 
need merely select the plants that have resisted the disease 
and save the seeds from those. Repeat this process of care- 
ful selection year after year, and the power of resistance 
will be developed more and more. Considerable progress 
has thus been made in developing a strain of flaxseed that 
shall be immune from flax wilt, cantaloupes that resist melon 
wilt, and cabbage that is free from black rot. Similar work 
with wheat and oats also seems promising. 
Some SPECIAL PLANT DISEASES 
There is a very large number of plant diseases, each usually 
confining itself to one particular species of plant. Fortu- 
nately for us, a cool, dry climate is not favorable to the de- 
velopment of disease-producing bacteria and fungi, and such 
states as North Dakota have comparatively little trouble 
except from grain rust and smut, and flax wilt. The follow- 
ing brief list includes about all that are of much consequence 
in the Northwest. 
Smuts attack wheat, oats, corn, and other grains, causing 
the black, powdery masses that are sometimes found in place 
