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presented during the growth of the primary mycelium is the
gradual tapering of the hyphae ; this tapering is of a two-fold
nature; the main trunk, or first portion emitted by the spore
produces secondary thinner branches, these in turn bear still
thinner branches, and this production of successively thinner
hyphae results in a complex structure, which may be compared
to the hranching of a tree, commencing with the trunk and
ending with the youngest and thinnest ramifications. The
second type of tapering is seen in the gradual attenuation of the
component hyphae; this is most conspicuous in the case of
elongated, unbranched hyphae, which from a basal width of
8—10 p. taper gradually towards the apex, which may not exceed
2 p in width. li a spore of 3Iucor laterit-ius, a species met with
on semi-putrid potatoes, be sown on a glass slip in a drop of
sterilized decoction of decayed potato, and. kept in a damp
atmosphere under a small bell-jar, growth pioceeds somewhat as
described above ; a dense mycelium showing the two aspects of
attenuation is developed; and as growth proceeds an irregular
reticulation is formed, due to the coalescence of originally
distinct lateral branches. This coalescence is not confined to
cases where two hyphae happen to meet in the ordinary coui'se
of growth, but in many instances, as described in detail by
Professor Marshall Ward in the instance of a species of
Botrytis} the hyphae attract each other, and may be deflected
from their previous course through a right angle or even more.
The peripheral hyphae usually elongate for some distance in
straight lines, the unknown iactor in connection with coalescence
being apparently absent from the youngest portions, and only
manifests itself at some distance behind the tips of the hyphae,
where it possibly determines first the origin of lateral branches,
and subsequently their direction. This yearning for coalescence
is not common to all lateral branches. The hyphae possess a
cell-wall but no transverse septa, hence the protoplasm is
continuous throughout the intricate mycelium, and, as would bo
expected, the cell-wall is exceedingly thin and yielding, and
becomes very pale blue with iodine, and very pale browmisli-
’ A lily-disease. Ánwils of Botany, vol. ii. pp. 319—378, 5 plates.
purple with cellulose reagents. After the vegetative mycelium
has acquired a certain amount of reserve material, one or more
of the thickest portions give origin to yet thicker branches
which grow erect; each erect branch at length becomes dilated
into a large sphere at its apex; into this sphere a considerable
amount of protoplasm, obtained from the vegetative mycelium,
becomes concentrated, and retained by the development of a
transverse septum at the base of the sphere where it passes into
its support. After these preliminaries, the reproductive phase
may be said to commence, the protoplasm undergoes differentiation,
resulting in the separation of lime which appears in the
form of a thin frosting outside the wall of the sphere or
sporangium ; another portion of the protoplasm becomes differentiated
into the broadly elliptical oonidia or spores; while a third
portion of the protoplasm, which may be considered as of no
value in the process of spore-making, remains in the form of
very thin, irregular strands in what may be termed the
intercellular spaces between the spores. Most species of the
Fhycotnycetes and Mucorini pass through the above phases
during their development, differing in minor points, as form of
oonidia, presence or absence of lime on sporangia, &o. The
above description covers many points in the development of a
typical member of the Myxogastres. The latter differ at the
starting-point in the first product of germination, being more
motile than in ifiscor, after coalescence of the cells to form a
plasmodium; the latter usually behaves somewhat similar to
the mycelium of M'ucor, advance of the mass being effected by
the protrusion of long tapering strands which at some distance
behind the tips coalesce to form a dense, irregular network;
every portion of a plasmodium, even the thinnest outlying
strands, are furnished with a distinct, thin, yielding membrane,
analogous at least to the membrane called the cell-wall, protecting
the protoplasm in the 3Iucor mycelium ; the two membranes
agree in origin, being secreted by the protoplasm; both become
blue with iodine, and pale dirty brownish-violet with “ chlor-zinc
iodide." The reproductive phase-consists in the conversion of
certain portions of the protoplasm into erect sporangia with the