216 PKACTICAL BOTANY 



work of food absorption. Food is carried through the tubular 

 cells to the parts of the mycelium that are above the food 

 material. 



202. Bread mold : effect upon the substratum. If a piece of 

 bread upon which bread mold is growing vigorously be kept 

 moist, the mold will not, usually, . continue to grow until the 

 bread is completely consumed. Either because of having se- 

 cured all the food it can extract from the bread, because of 

 having secreted substances that prevent its further growth, or 

 because of being unable to hold its own with other organisms 

 (molds and bacteria), the bread, mold after a time ceases to 

 grow. Other molds and bacteria may appear, one kind follow- 

 ing another for weeks, until the decay of the bread is almost 

 or quite complete. If kept tightly sealed, however, growth 

 stops before all the food material is used. Molds often grow 

 for a time in jars of fruit, forming upon the top of the fruit 

 a coating which remains until the jar is opened. If this coat- 

 ing is removed and a fresh supply of air is admitted, a new 

 growth soon appears. 



203. Bread mold: asexual reproduction. In addition to vege- 

 tative reproduction by means of stolons, this mold also repro- 

 duces itself both asexually and sexually. There arise from the 

 main body of the mycelium upright hyphae, upon the ends of 

 which sporangia are produced (Fig. 176). The upright stalks 

 are called sporangiophores (meaning " sporangia bearers"). In 

 the development of the sporangium, first a transverse wall cuts 

 off a small tip of the upright stalk. This tip cell grows rapidly 

 until it has become a large spherical body. Meanwhile the 

 transverse walr has extended into the spherical sporangium, 

 thus producing a little column (the columella) upon which the 

 sporangium contents rest. The protoplasm of the sporangium 

 divides into many small spores, which, when the sporangium 

 wall breaks, are scattered widely into the air. The musty odor 

 which is detected when we smell Arnold may be due to the 

 presence of large numbers of these spores, or to gases that 

 have been produced within, the nutrient material. 



