[CHAPTER XIX.]
FUNGI: MUCOR AND SAPROLEGNIA.
Mucor.
387. In the chapter on growth, and in our study of protoplasm, we have become familiar with the vegetative condition of mucor. We now wish to learn how the plant multiplies and reproduces itself. For this study we may take one of the mucors. Any one of several species will answer. This plant may be grown by placing partially decayed fruits, lemons, or oranges, from which the greater part of the juice has been removed, in a moist chamber; or often it occurs on animal excrement when placed under similar conditions. In growing the mucor in this way we are likely to obtain Mucor mucedo, or another plant sometimes known as Mucor stolonifer, or Rhizopus nigricans, which is illustrated in [fig. 191]. This latter one is sometimes very injurious to stored fruits or vegetables, especially sweet potatoes or rutabagas. [Fig. 190] is from a photograph of this fungus on a banana.
388. Asexual reproduction.—On the decaying surface of the vegetable matter where the mucor is growing there will be seen numerous small rounded bodies borne on very slender stalks. These heads contain the gonidia, and if we sow some of them in nutrient gelatine or agar in a Petrie dish the material can be taken out very readily for examination under the microscope. Or we may place glass slips close to the growing fungus in the moist chamber, so that the fungus will develop on them, though cultures in a nutrient medium are much better. Or we may take the material directly from the substance on which it is growing. After mounting a small quantity of the mycelium bearing these heads, if we have been careful to take it where the heads appear quite young, it may be possible to study the early stages of their development. We shall probably note at once that the stalks or upright threads which support the heads are stouter than the threads of the mycelium.
Fig. 190.
Portion of banana with a mould (Rhizopus nigricans) growing on one end.
These upright threads soon have formed near the end a cross wall which separates the protoplasm in the end from the remainder. This end cell now enlarges into a vesicle of considerable size, the head as it appears, but to which is applied the name of sporangium (sometimes called gonidangium), because it encloses the gonidia.
At the same time that this end cell is enlarging the cross wall is arching up into the interior. This forms the columella. All the protoplasm in the sporangium now divides into gonidia. These are small-rounded or oval bodies. The wall of the sporangium becomes dissolved, except a small collar around the stalk which remains attached below the columella (fig. 192). By this means the gonidia are freed. These gonidia germinate and produce the mycelium again.
