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mm
distinctions depending more especially on the mode of branching
and colour. The point of interest in the present connection is the
mode of spore formation. Without entering into details, the protoplasm,
immediately preceding spore formation, becomes arranged
on the branches as a peripheral layer of cells enclosed in cell-
walls, which, in the case of Geratium hydnoides, give a cellulose
reaction when young. Owing to local growth, the central portion
of the free side of each cell grows outwards in the form of a
slender elongated cylinder until it measures about 10 p in
length by about S p in diameter; the next change consists
in the expansion of the free end of this outgrowth which continues
until it assumes in G. hydnoides, a broadly elliptical form,
about 10 X 6—7 p in size; into this swollen apical portion the
whole of the protoplasm then passes through the stalk from the
parent cell, after which a transverse septum is formed in the
stalk-like portion close up to its swollen apex, which eventually
breaks away at the septum as a mature spore. In G. hydnoides
the stalks persist after the spores have fallen away, each closed
at the apex by the septum which formed the line of dehiscence,
and the homology with the formation of conidia or spores in the
Basidiomycetes is perfect. In each case we find a cell richly
supplied with protoplasm giving origin by local growth to one or
more thin spine-like processes, each of which becomes much
enlarged at its apex; into these enlarged portions all the protoplasm
from the mother-cell becomes concentrated and retained
by the formation of a septum across the stalk close to the
swollen apex, which eventually falls away at the septum as a
ripe spore. The first appearance of a transverse septum being
for the purpose of isolating a mass of protoplasm concentrated
for purposes directly concerned with reproduction suggests the
idea, if nothing more, that the Myxogastres are in touch with
other acknowledged members of the vegetable kingdom. The
remaining species of Ceratmm show the same mode of spore
formation, but in G. arhuseula, B. and Br., a very fine much-
branched species, the thin outgrowth bearing the spore at its
apex is much larger than in C. hydnoides, and the transverse
septum is even more distinct, while in G.filiforme, B. and Br., the
slender stalk-like outgrowth measures from 18—20 p in length,
and after having become inflated at the apex and absorbing the
protoplasm from the parent cell, is cut off from the latter, first
by a septum close to the parent cell; this is followed by the
formation of a second septum close to the base of the swollen
apical portion or spore.
9. In the coalescence of the naked cells to form a plasmodium
being the result of conjugation between the component cells,
thus presenting features in common with the primitive forms
included in the group Zygosporeae. The reasons for the above
statement are as follows—The frequent occurrence of forms
intermediate between well-marked, but closely allied species,
suggested the idea of hyhridity, especially as the supposed
hybrids varied in their degree of morphological agreement with
one or other of the two species between which they were
intermediate. With the object of ascertaining whether hybrids
were formed in nature, the young plasmodia of Physarum
leucopus and Physarum leucophaeum were so placed that the
plasmodia of the two became blended together at the point of
contact; this experiment resulted in the formation'of sporangia
intermediate between the two species from the blended ^portion
of plasmodium, whereas sporangia typical of the two rspecies
respectively were produced from those portions of plasmodia
farthest removed from the point of contact of the two plasmodia.
Without entering into minute specific details, it will be sufficient
to state that Physancm leucophaeum has a dark-brown
stem and a thin eapillitium with few knots of lime, whereas
Physarum leucopus has a white stem and stout eapillitium with
numerous large knots of lime. The hybrid has a white stem
and a slender eapillitium with few knots of lime. In the Kew
herbarium there is a specimen collected at Highgate by Dr.
Cooke, which agrees exactly with the hybrid described above,
and which appears to have specially attracted the attention of
Mr. Arthur Lister, who in going over the collection of Myxogastres,
made a careful drawing of the specimen, adding,
“ Physarum leticophacu'm with a pale stalk.” I have also produced
a hybrid from two species of Trichia. Mr. Harold