6 
The Colorado Experiment Station. 
stuff so that all of the offspring is retained in one place, the colony 
first appears to the naked eye as a tiny speck which grows to the size 
of a pin head or larger depending upon the species and the en¬ 
vironmental conditions. (See Plates II and III.) 
Any growth of bacteria, yeasts or molds is spoken of as a 
culture; if this is made up of several different kinds of organisms, 
it is referred to as a mixed culture (Plate III, 2.), but if it is com¬ 
posed of only one species, then it is termed a pure culture (Plate 
III, 1). Thus, we have pure culture starters for butter, cheese 
and vinegar. 
Although we do not ordinarily think of plants as being able 
to move about, some bacteria, notably the rods and spirals, possess 
this power in a very marked degree. They are provided with very 
fine, hair-like appendages, known as flagella, which extend out¬ 
ward from the body of the cell like the legs of a “grand-daddy- 
long-legs.” Sometimes they come out from all sides of the germ 
and again only from the ends. These are kept moving rapidly all 
of the time with a lashing motion, much as a fish moves its fins, 
and by this means the bacteria are able to swim from place to place 
through the body fluids, decaying matter, milk, water, etc. 
Many bacteria and molds, as well as some yeasts, develop bodies 
which are known as spores. These are much more resistant to ex¬ 
tremes of heat, drought, famine and chemicals than the ordinary or 
vegetative forms and serve to tide the organism over unfavorable 
periods which would have meant almost certain death and anni¬ 
hilation of the species. Whereas many bacilli in the vegetative 
stage are killed by ten minutes exposure to the temperature of 140 
degrees Fahrenheit, some spores can withstand the temperature of 
boiling water for upward of sixteen hours. Many soil organisms 
possess spore stages, but, fortunately for man and beast, the num¬ 
ber of disease producing bacteria which have this property is small. 
Source of Plant Foods. 
Between 97 and 98 per cent, of the weight of a growing plant 
is made from the carbon dioxide gas of the air and the water in 
the soil. The supply of these two substances is unlimited. The 
remaining 2 to 3 per cent., which constitutes the ash, is obtained 
largely from the soil, and the elements which compose this portion 
occur in limited quantities only. Year after year these mineral sub¬ 
stances are appropriated by plants, and this constant drain for count¬ 
less centuries would have exhausted the supply most certainly, were 
it not being replenished from some source. That this loss is re¬ 
stored is evidenced by the fact that our native plants continue to 
