The life-history and cytology of Didymium
nigripes have been worked out in detail. The organism grows well in carrot-agar and takes about a fortnight to six weeks to complete its life- history, the
time required depending very largely on external conditions.The spore coat is ruptured by osmotic pressure and the single nucleus then divides karyokinetically, four chromosomes being present. The centrosome arises in the nucleus and passes outwards, leaving behind it the 'Verbindungstuck'. Division of
centrosome and Verbindungstuck precede the nuclear
division. Nuclear division is followed by division
of the protoplast, and two swarm:- cell emerge from
the spore coat. The centrosome subsequently functions as the blepharoplast.After three or four divisions the swarm -cell
withdraws the flagellum, 'Verbindungsttick' and blepharoplast and becomes a myxamoeba. The rnyxamoebae
fuse in pairs to form the zygote or young plasmodium.The young plasmodium can ingest swarm-cells
and unfused myxamoebae, and can also coalesce with
smaller plasmodia. About five or six days after germination, the larger plasmodia exert a distinct attraction on the uninucleate plasmodia in their
neighbourhood and these coalesce with them in large
numbers,Nuclear divisions are 'comparatively rare in
the young plasmodium. The division is karyokinetic;
intracuclear, and no centrosomes are present, Eight
chromosomes are formed. The plasmodium increases in
size by coalescing with any small plasmodia it
encounters,The stalk of the sporangium is formed by the
degeneration of large masses of protoplasm. The
wall- and ca._ pilitium probably arise as a result of a chemico-physical action taking place on the surface
of protoplasm exposed to air and controlled by the
protoplasm itself.Cleavage of the sporogenous protoplasm and
meiosis proceed. simultaneously, The meiosis is typical and consists of the usual heterotype and homo - type divisions, Both divisions are intra-nuclear,
without centrosomes and with four chromosomes. In
the heterotype division. the chromosomes are U-shaped,
in the homotype one they are spherical, The final
cleavage into singel spores takes place during the
concluding stages of the homotype division.Didymium Whines is considered to be a
more advanced type than Reticularia Lycoperdon, because of the presence of myxamoebae, the fusion of
amoeboid gametes, and the formation of a true
capillitium,
