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 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 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 (granular substance 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 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 ciliæ show themselves, 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 (Plate X. fig. 208).