1881. ] Bacteria as a Cause of Disease in Plants. 527 
BACTERIA AS A CAUSE OF DISEASE IN PLANTS. 
BY PROFESSOR T. J. BURRILL. 
peas diseases of animals are now positively known to be 
‘ due to the action of the minute organisms commonly known 
as bacteria, They are spoken of as “disease germs” or “ spores,” 
and the “germ theory” of disease is very fully discussed in 
medical literature. Among the best proved examples that the 
so-called germs are the actual cause of disease, we may cite 
anthrax in cattle, malignant pustule in man, and the diseases of 
swine and fowl ordinarily known as cholera. Many other con- 
tagious diseases of man and the domestic animals are scarcely 
less clearly known to be due to bacteria, but it has not been 
shown that they also cause disease and death of plants, except as 
recently announced by the writer in case of “ blight” in pear and 
apple trees (August, 1880, American Association for the Advance- 
Healthy Pear Bark, showing cells filled with starch. Magnified 125 times. — 
ment of Science). I am now able to add the “yellows” of the 
peach with much confidence, without, however, the full investiga- 
tion given to the former disease. 
In 1877 I observed in the fluids of blighting pear trees, great 
numbers of minute, moving things which were not clearly identi- 
fied as bacteria until the following year. Their presence was 
uniformly detected in every examination made (and they were 
numerous) during the summer of 1878, and the fact was reported 
to the Illinois State Horticultural Society, in December of that 
year (Transactions, p. 79). Investigations were not further pros- 
