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 thought they were productions of the dead matter upon which they grew, but now we know that a mold, 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_. _Favorable 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 mold on each. Note the result from day to day. Moisten a third piece of bread with weak copper sulfate (blue vitriol) or mercuric chlorid solution, sow mold, 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. [Illustration: FIG. 271.--MUCOR MUCEDO, showing habit.] [Illustration: FIG. 272.--SPORES OF MUCOR, some germinating.] _Mold._--One of these molds (_Mucor mucedo_), which is very common on all decaying fruits and vegetables, is shown in Fig. 271, somewhat magnified. When fruiting, this mold appears as a _dense mass of long white hairs_, often over an inch high, standing erect from the fruit or vegetable on which it is growing. The life of this mucor begins with a minute rounded spore (_a_, Fig. 272), which lodges on the decaying material. When the spore germinates, it sends out a delicate thread that grows rapidly in length and forms very many branches that soon permeate every part of the substance on which the plant grows (_b_, Fig. 272). One of these threads is termed a _hypha_. All the threads together form the _mycelium_ of the fungus. The mycelium disorganizes the material in which it grows, and thus the mucor plant (Fig. 271) is nourished. It corresponds physiologically to the roots and stems of other plants.