Colorado Plant Diseases 
9 
slime molds because of their slimy appearance in one stage of their 
life history. Slime molds are also very small and primitive plants 
although much larger than bacteria. At one stage in their develop- 
ment they have the appearance of a slimy particle of jelly-like sub- 
stance. This structure is known as a plasmodium. A plasmodium 
has the ability to move about by a peculiar rolling or flowing move- 
ment. When it grows old or meets with unfavorable conditions the 
plasmodium breaks up into numerous spores which can live over 
unfavorable conditions. When conditions are again favorable the 
spores germinate to form bodies (amoebae) similar to a plasmodium 
but much smaller. A plasmodium is formed by a number of these 
amoebae uniting with one another to form a single body. 
Only a few of the slime molds cause plant diseases. Most of the 
forms live on dead and decaying wood. A few forms, however, may 
gain entrance into the roots or stems of plants and cause a disease. 
Powdery scab of potatoes and club root of cabbage are the most 
important diseases caused by slime molds. 
Fungi — The fungi 
make up a large and 
varied group of plants 
and are responsible for 
about 90% of the com- 
mon plant diseases. In 
addition to those fungi 
which cause plant dis- 
eases there are thou- 
sands of other kinds 
which spend their entire 
life on decaying plants 
and other dead organic 
matter. 
Most plants manufac- 
ture their own carbo- 
hydrate or starchy food 
by means of the green coloring matter (chlorophyll) found in their 
leaves. The fungi, however, as well as the bacteria and slime molds 
do not have green coloring matter and consequently can not make 
their own food. Since these organisms require carbohydrates for 
their nourishment it is evident that they must obtain it from some 
source in an already manufactured condition. 
Some fungi obtain their nourishment from decaying organic 
matter, while others obtain it directly from the living chlorophyll 
