STUDIES LV CRYPTOGAMS 



189 



Fig. 274. — MucoR. 



a, sporangium; i, 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 SDorangium, 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 favourable 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 favourable 

 ground, so that the fungus is provided with 

 another means of carrying itself over unfavour- 

 able seasons, as wintei. 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- 

 gium directly or growing out as mycelium. 

 The zygospores of the mucors form one of the most interesting 

 and instructive objects among the lower plants. They are, how- 

 ever, very difficult to obtain. One of the mucors \Sporodinia 



Fig. 273. — Mucor, 

 showing formation 

 of zygospore on 

 th,e right; germi- 

 nating zygospore 

 on the left. 



