higher secondary - first year - botany - Textbooks Online

called sporangiophores arise from the mycelium. These sporangiophores are
hyaline and do not produce rhizoids at their base. The apex of the sporangiophore
enlarges to form a vesicle which may be globose or spherical, multispored and
columellate structure - the sporangium. As the hypha begins to swell, the
protoplasmic contents migrate to its tip and accumulate there. The protoplasm
differentiates into a central vacuolated region and an outer fertile dense peripheral
region containing large number of nuclei. The central vacuolated region is separated
from the peripheral
region by a cleft or
furrow and this
furrow later
develops into a wall.
This central sterile
region is called
columella. The
peripheral fertile
region forms spores
as follows : The
peripheral
protoplasm now
gives rise to a
number of small,
multi-nucleate,
angular masses by
cleavage. Each
multinucleate mass
becomes rounded
off and is covered by
a wall forming a
spore. The spore
wall thickens and
darkens. The wall of
the sporangium is
thin and brittle. The
columella swells due
to the accumulation
of a quantity of fluid
and exerts a
considerable
pressure on the wall
of the sporangium.
40