272 COOKE, ON MICROSCOPIC FUNGI, 
watery, and the terminal vesicles have their walls thickened, so as to 
resemble, on a casual observation, granules of starch. Dr. de Bary 
conceives that these appendages serve a similar purpose to the 
tendrils or suckers of climbing phanerogamic plants; 7.e. to fix the 
mycelium to the cells which are to supply the parasite with nourish- 
ment. As these appendages are always present, it is easy to discover 
the mycelium wherever it exists among the tissues of an affected 
plant. 
“The white pustules already alluded to contain the fruit of the 
parasite. Bundles of clavate or club-shaped tubes are produced upon 
the mycelium beneath the epidermis of the infested plant, forming a 
little tuft or cushion, with each tube producing at its apex reproduc- 
tive 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 re- 
peated 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. 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 separat- 
ing 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 
in further confirmation. Ifthe conidia (white spherical bodies ejected 
from the pustules of the ‘white rust’) are sown in a drop of water 
on a glass slide, being careful to immerse them entirely, they will 
rapidly absorb the water and swell; soon afterwards a large and 
obtuse papilla, resembling the neck of a bottle, is produced at one of 
the extremities. At first vacuoles are formed in the contents of each 
conidium; as these disappear, the whole protoplasm (granular sub- 
stance filling the conidium) becomes separated by very fine lines of 
demarcation into from five to eight polyhedric portions, each with a 
faintly coloured vacuole in the centre. These portions are so many 
zoospores. Some minutes after the internal division, the papilla swells 
and makes itself an opening, through which the zoospores are expelled 
one by one, without giving any signs of movement of their own. 
They take a flat disc-lke or lenticular form, and group themselves 
about the opening, whence they have been expelled, in a globular 
mass. Soon, however, they begin to move, vibratile cilie show them- 
selves, and by means of these appendages the entire globule oscillates, 
the zoospores disengage themselves from each other, the mass is 
broken up, and each zoospore swims off on its own account. 
“ The free zoospores are of the form of a plano-convex lens, obtuse 
at the edge. Beneath the plane face, out of the centre, and towards 
that point of the margin which during the movement of the zoospore 
is foremost, is a disc-shaped vacuole with two cilizw of unequal length 
attached to its margin; the shorter cilia is directed forwards, and 
the longer in the opposite direction, during the evolutions of the 
zoospores. 
“The zoospores are produced within from an hour and a half to 
three hours after the sowing of the conidia in water. They are never 
absent if the conidia are fresh, or even a month old, but beyond this 
