Fucus.—These are rather large specialized algæ belonging to the group known as brown seaweeds and found attached by a disk to the rocks of the seashore just below high tide (Fig. [269]). They are firm and strong to resist wave action and are so attached as to avoid being washed ashore. They are very abundant algæ. In shape the plants are long, branched, and multicellular, with either flat or terete branches. They are olive-brown. Propagation is by the breaking off of the branches. No zoöspores are produced, as in many other seaweeds; and reproduction is wholly sexual. 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 coloured 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.
Fig. 270.—Nitella.
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, in favourable 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.
Fungi
Some forms of fungi are familiar to every one. Mushrooms and toadstools, with their varied forms and colours, are common in fields, woods, and pastures. In every household the common moulds 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 thought they were productions of the dead matter upon which they grew, but now we know that a mould, as any other plant, cannot originate spontaneously; it must start from something which is analogous to a seed. The “seed” in this case is a spore. A spore may be produced by a vegetative process (growing out from the ordinary plant tissues), or it may be the result of a fertilization process.
Favourable conditions for the growth of fungi.—Place a piece of bread under a moist bell jar and another in an uncovered place near by. Sow mould on each. Note the result from day to day. Moisten a third piece of bread with weak copper sulphate (blue vitriol) or mercuric chloride solution, sow mould, cover with bell jar, note results, and explain. Expose pieces of different kinds of food in a damp atmosphere and observe the variety of organisms appearing. Fungi are saprophytes or parasites, and must be provided with organic matter on which to grow. They are usually most abundant in moist places and wet seasons.