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The antheridia, bearing sperm-cells, and the oögonia, each bearing eight egg-cells, are sunken in pits or conceptacles. These pits are aggregated in the swollen lighter colored tips of some of the branches (s, s, Fig. 269). The egg-cells and sperm-cells escape from the pits and fertilization takes place in the water. The matured eggs, or spores, reproduce the fucus plant directly.

Fruiting branches at s, s. On the stem are two air-bladders.

Nitella.—This is a large branched and specialized fresh-water alga found in tufts attached to the bottom in shallow ponds (Fig. 270). Between the whorls of branches are long internodes consisting of a single cylindrical cell, which is one of the largest cells known in vegetable tissue. Under the microscope the walls of this cell are found to be lined with a layer of small stationary chloroplastids, within which layer the protoplasm, under favorable circumstances, will be found in motion, moving up one side and down the other (in rotation). Note the clear streak up the side of the cell and its relation to the moving current.

Some forms of fungi are familiar to every one. Mushrooms and toadstools, with their varied forms and colors, are common in fields, woods, and pastures. In every household the common molds are familiar intruders, appearing on old bread, vegetables, and even within tightly sealed fruit jars, where they form a felt-*like layer dusted over with blue, yellow, or black powder. The strange occurrence of these plants long mystified people, who