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12G IIICEOSCOPIC FUXGI.
these appendages are always present^ it is easy to
discover the mycelium wherever it exists amongst
the tissues of an afiected plant.
The white pustules already alluded to contain the
fi'uit of the parasite. Bundles of clavate or clubshaped
tubes are produced upon the mycelium beneath
the epidermis of the infested plants forming
a little tuft or cushion, with each tube producing
at its
apex reproductive cells, designated " conidia.''^
These conidia appear to be produced in the following
:— manner The tips of the clavate tubes generate
them in succession. At first a septum, or
partition, divides from the lower portion of the
tube a conidium cell; this becomes constricted at
the septum and assumes a spherical shape, at
length only attached by a short narrow neck.
Beneath this again the same process is repeated
to form another and another conidium in succession,
until a bead-like string of conidia surmount each
of the tubes from which they are produced (plate
X. fig. 200). At length the distended epidermis
above is no longer able to bear the pressure of the
mass of engendered conidia within, and is ruptured
irregularly, so that the conidia, easily separating
from each other at the narrow neck, make their
escape.
As long since as 1807, M. Prevost described the
zoospores, or moving spores, of these conidia, and
his observations were confirmed by Dr. de Bary three
years since,
and are now adverted to by him again