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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 ; i. e ., to 
fix the mycelium to the cells which are to supply the parasite 
with nourishment. As these appendages are always present, 
it is easy to discover the mycelium wherever it exists amongst 
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, each tube en- 
gendering at its apex reproductive cells, designated “ conidia.” 
These conidia appear to result 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 j 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 succes- 
sion, 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 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 now adverted 
to by him again in further confirmation. If the 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 (gra- 
nular substance within the conidium) becomes separated by 
very fine lines of demarcation, into from five to eight polyhe- 
dric 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 disk-like 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 
