filament may be effected by the attacks of
another organism.

[Sidenote: Spores.]

A very characteristic method of reproduction is that of spore-formation,
and these minute reproductive bodies, which represent a resting stage of
the organism, are now known in many forms. Formerly two kinds of spores
were described, _arthrospores_ and _endospores_. An arthrospore, however,
is not a true spore but merely an ordinary vegetative cell which separates
and passes into a condition of rest, and such may occur in forms which form
endospores, _e.g._ _B. subtilis_, as well as in species not known to form
endospores. The true spore or endospore begins with the appearance of a
minute granule in the protoplasm of a vegetative cell; this granule
enlarges and in a few hours has taken to itself all the protoplasm,
secreted a thin but very resistive envelope, and is a ripe ovoid spore,
smaller than the mother-cell and lying loosely in it (cf. figs. 6, 9, 10,
and 11). In the case of the simplest and most minute Schizomycetes [v.03
p.0162] (_Micrococcus_, &c.) no definite spores have been discovered; any
one of the vegetative micrococci may commence a new series of cell by
growth and division. We may call these forms "asporous," at any rate
provisionally.

[Illustration: FIG. 9.

A. _Bacillus anthracis._ (After de Bary) Two of the long filaments (B, fig.
10) in which spores are being developed. The specimen was cultivated in
broth, and spores are drawn a little too small--they should be of the same
diameter transversely as the segments.

B. _Bacillus subtilis._ (After de Bary.) 1, fragments of filaments with
ripe spores; 2-5, successive stages in the germination of the spores, the
remains of the spore attached to the germinal rodlets.]

[Illustration: FIG. 10.--_Bacillus subtilis_. (After Strasburger.) A.
Zoogloea pellicle. B. Motile rodlets. C. Development of spores.]

The spore may be formed in short or long segments, the cell-wall of which
may undergo change of form to accommodate itself to the contents. As a rule
only one spore is formed in a cell, and the process usually takes place in
a bacillar segment. In some cases the spore-forming protoplasm gives a blue
reaction with iodine solutions. The spores may be developed in cells which
are actively swarming, the movements not being interfered with by the
process (fig. 4, D). The so-called "Koepfchenbacterien" of older writers
are simply bacterioid segments with a spore at one end,