SECT. 1 



CRYPTOGAMS 



385 



Tlies(3 escape by the .swelling of a substance \\liicli lies between the spores ami the 

 bursting of the sporangial wall. In Pilobulus, wliich occurs commonly on dung, 

 the sporangium is forcibly cast off from the turgid sporangiophore which bursts at 

 the columella. According to HarpkPw the spores of Piloholus are binucleate, wliile 

 those of Sporodinia (Fig. 314) are multinucleate. 



Fic. 313.— i, Mucor Mucedo. A sporangium in optical longitudinal .section ; c, eoluniplla ; m, wall 

 of sporangium ; .sj), spore.s. 2, Mucor mucilagineus. A sporangium sliodding its spores; tlie 

 wall (in) is ruptured, and the mucilaginous substance between tlie spores (?) is greatly swollen. 

 (After Brefeld, 1 x 2-2.5, 2 x 300, from v. T.avel, Pilze.) 



Under certain conditions, instead of asexual sporangia, organs of sexual repro- 

 duction are produced. The hyphae of the mycelium then give rise to lateral, club- 

 shaped branches. When the tips of two such branches come into contact, a 

 conjugating cell or coenogamete is cut off from each by a transverse wall (Fig. 315), 

 The two gametes thereupon coalesce, and fuse into a zygospore, the outer wall of 

 which is covered with warty protuberances. As regards the behaviour of the 

 nuclei in the process of conjugation, only 

 some facts for Sporodinia are known. 

 According to Lendner, a larger sexual 

 nucleus is ditlerentiated in each of the 

 multinucleate gametes. The two sexual 

 nuclei fuse in the centre of the zygospore, 

 while the numerous small peripheral nuclei 

 take no part in the process. They still 

 divide, however, and probalily play a part 

 in the formation of the wall of the 

 zygospore. After a period of rest the 

 zygospore germinates, developing a germ- 

 tube, which may at once bear a sporangium 

 (Fig. 315, 5). • 



Blakeslee's (^•') demonstration of the 

 dioecious (heterothallic) nature of the 

 mycelium of most Mucorineae, for example Mucor Mucedo and Rhizopus nigricans, is 

 of great interest. The formation of zygospores only takes place when male and 

 female mycelia come in contact. In other Mucorineae (homothallic, e.g. Sporodinia 

 grandis) the two conjugating gametes may arise on the same mycelium. Exception- 

 ally in heterothallic species, sucli as I'hycomyces nitens, a homothallic mycelium 

 may appear. This arises from a zy^ ospore, the germ-tube of wliicli has not, as is the 

 rule, formed a sporangium at once. 



2c 



Fig. 314. — Sporodinia grandis. Median section 

 of a ripe .sporangium. The spores are 

 multimicleate. (After Harper, x 42-5.) 



