CHAPTER XXIII 
SMALLEST PLANTS (BACTERIA) 
264. Bacteria. — Bacteria are the smallest of all plants, 
— so small that they can be seen singly only through the aid 
of a powerful microscope. We do not know all about their 
life processes, but we have learned much about their effect. 
We constantly hear about these plants, either under their 
correct name, bacteria , or under the names of germs or 
microbes. Two incorrect ideas concern¬ 
ing bacteria are prevalent, — one, that 
bacteria are animals, and the other, that 
all are harmful. It is definitely known 
that bacteria are plants; that small as 
they are, they are among the most im¬ 
portant plants in the world; that most 
of them are helpful, and only a few harm¬ 
ful. They are, however, so much like 
the one-celled animals (protozoa) that 
the word germ is not unnaturally used 
to cover both. 
265. Shape and Size of Bacteria. — Bacteria, according to 
their shape, are grouped into three classes: (1) round 
(the cocci); (2) rod-shaped, like a short unsharpened pencil 
(the bacilli); (3) those that are shaped like a corkscrew 
(the spirilla). Most of the names for the different bacteria 
contain one or another of these words, thus indicating the 
shape of the bacterium 1 under discussion. The spirilla 
and. the bacilli often have on one or both ends tiny thread- 
1 Bacterium, singular of bacteria. 
309 
A, cocci; B, bacilli; 
C, spirilla; D, bacillus 
with flagella. 
