8 
Colorado Experiment Station 
Some forms of bacteria are able to move about in water and 
plant juices by means of little hair-like attachments to their body. 
These hair-like attachments, known as flagella, move rapidly back 
and forth, propelling the bacterium through the liquid. These forms 
which are capable of motion are the ones which commonly cause 
plant diseases. Other forms do not have the power of motion and 
depend on outside agencies such as wind and moving water to 
carry them from place to place. 
Bacteria gain entrance into the leaves, stems and roots of plants 
by means of breathing pores or injuries. After gaining entrance 
the bacteria live on the substance of the plant, either killing it (or 
parts of it) or causing it to make abnormal growth, thus bringing 
about a diseased condition. 
Fire blight of apples and pears, stem blight of alfalfa, wilt of 
squashes and melons, black rot of cabbage and crown gall of many 
plants are a few of the serious diseases caused by bacteria. 
Slime Molds — Another group of plants which sometimes cause 
plant diseases are the slime molds (Myxomycetes). They are called 
The life history of a typical slime mold. A — A group of amebae 
fusing to form a plasmodium. E — A plasmodium. (After Curtis, 
Henry Holt & Company.) 
