. Beginners' botany. Botany. STUDIES IN CRYPTOGAMS 189. Fig. 274. — Mucor. ay sporangium; b> sporangium bursting; c, columella. delicate stalk, the sporangiophore. The stalk is separated from the sporangium by a wall which is formed at the base of the spo- rangium. This wall, however, does not extend straight across the thread, but it arches up into the sporangium like an inverted pear. It is known as the col- umella, c. When the sporangium is placed in water, the wall immediately dissolves and allows hundreds of spores, which were formed in the cavity within the sporangium, to escape, b. A
. Beginners' botany. Botany. STUDIES IN CRYPTOGAMS 189. Fig. 274. — Mucor. ay sporangium; b> sporangium bursting; c, columella. delicate stalk, the sporangiophore. The stalk is separated from the sporangium by a wall which is formed at the base of the spo- rangium. This wall, however, does not extend straight across the thread, but it arches up into the sporangium like an inverted pear. It is known as the col- umella, c. When the sporangium is placed in water, the wall immediately dissolves and allows hundreds of spores, which were formed in the cavity within the sporangium, to escape, b. All that is left of the fruit is the stalk, with the pear-shaped columella at its summit, c. The spores that have been set free by the breaking of the sporangium wall are now scattered by the wind and other agents. Those that lodge in favorable places be- gin to grow immediately and reproduce the fungus. The others soon perish. The mucor may continue to reproduce itself in this way indefi- nitely, but these spores are very delicate and usually die if they do not fall on favorable ground, so that the fungus is provided with another means of carrying itself over unfavora- ble seasons, as winter. This is accomplished by means of curious thick-walled resting-spores or zygospores. The zygospores are formed on the mycelium buried within the substance on which the plant grows. They originate in the following way : Two threads that lie near to- gether send out short branches, which grow toward each other and finally meet (Fig. 273). The walls at the ends, a, then disappear, allow- ing the contents to flow together. At the same time, however, two other walls are formed at points farther back, b, b, separating the short section, c, from the remainder of the thread. This section now increases in size and becomes covered with a thick, dark brown wall orna- mented with thickened tubercles. The zygo- spore is now mature and, after a period of rest, it germinates, either producing a sporan-
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Keywords: ., bookauthorbai, bookcentury1900, bookdecade1900, booksubjectbotany
