ears equally capable of performing all the physiological functions
of the species has led most authorities, however, to regard it as the
individual--a view which cannot be consistent in those cases where a simple
or branched filamentous series exhibits differences between free apex and
fixed base and so forth. It may be doubted whether the discussion is
profitable, though it appears necessary in some cases--_e.g._ concerning
pleomorphy--to adopt some definition of individual.

[Illustration: FIG. 12.

A. _Myxococcus digelatus_, bright red fructification occurring on dung.

B. _Polyangium primigenum_, red fructification on dog's dung.

C. _Chondromyces apiculatus_, orange fructification on antelope's dung.

D. Young fructification.

E. Single cyst germinating.

(A, B, after Quehl; C-E, after Thaxter.) From Strasburger's _Lehrbuch der
Botanik_, by permission of Gustav Fischer.]

_Myxobacteriaceae._--To the two divisions of bacteria, Haplobacterinae and
Trichobacterinae, must now be added a third division, Myxobacterinae. One
of the first members of this group, _Chondromyces crocatus_, was described
as long ago as 1857 by Berkeley, but its nature was not understood and it
was ascribed to the Hyphomycetes. In 1892, however, Thaxter rediscovered it
and showed its bacterial nature, founding for it and some allied forms the
group Myxobacteriaceae. Another form, which he described as _Myxobacter_,
was shown later to be the same as _Polyangium vitellinum_ described by Link
in 1795, the exact nature of which had hitherto been in doubt. Thaxter's
observations and conclusions were called in question by some botanists, but
his later observations and those of Baur have established firmly the
position of the group. The peculiarity of the group lies in the fact that
the bacteria form plasmodium-like aggregations and build themselves up into
sporogenous structures of definite form superficially similar to the cysts
of the Mycetozoa (fig. 12). Most of the forms in question are found growing
on the dung of herbivorous animals, but the bacteria occur not only in the
alimentary canal of the animal but also free in the air. The Myxobacteria
are most easily obtained by keeping at a temperature of 30-35deg C. in the
dark dung which has lain exposed to the air for at least eight days. The
high temperature is favourable to the growth of the bacteria but [v.03
p.0164] inimical to that of the fungi which are so common on this
substratum.