minute spheres, rods, or spirals, with no further discernible
structure, sometimes motile and sometimes stationary, sometimes
producing spores and sometimes not, and multiplying universally by
binary fission. With all the development of the modern microscope
we can hardly say more than this. Our advance in knowledge of
bacteria is connected almost wholly with their methods of growth
and the effects they produce in Nature.

ANIMALS OR PLANTS?

There has been in the past not a little question as to whether
bacteria should be rightly classed with plants or with animals.
They certainly have characters which ally them with both. Their
very common power of active independent motion and their common
habit of living upon complex bodies for foods are animal
characters, and have lent force to the suggestion that they are
true animals. But their general form, their method of growth and
formation of threads, and their method of spore formation are
quite plantlike. Their general form is very similar to a group of
low green plants known as Oscillaria. Fig. 17 shows a group of
these Oscillariae, and the similarity of this to some of the
thread-like bacteria is decided. The Oscillariae are, however,
true plants, and are of a green colour. Bacteria are therefore to-
day looked upon as a low type of plant which has no chlorophyll,
[Footnote: Chlorophyll is the green colouring matter of plants.]
but is related to Oscillariae. The absence of the chlorophyll has
forced them to adopt new relations to food, and compels them to
feed upon complex foods instead of the simple ones, which form the
food of green plants. We may have no hesitation, then, in calling
them plants. It is interesting to notice that with this idea their