FUNGI, SEX IN MUCORS 279 



which would be of opposite sex natures can meet and conjugate. 

 Under natural conditions these two strains or sets of mycelia of 

 opposite nature are sometimes growing mixed together, but more 

 often, probably, the two strains are growing separately. If one 

 obtains a culture of only one strain on the bread no zygospores 

 will be produced. But if the mixed strains are obtained, then 

 zygospores will be produced in number down in the lower part of 

 the vessel where it is moist, usually in small spaces between the 

 paper and the wall of the vessel or bread. It will be remembered 

 that the plant body of an alga or a fungus is called a thallus. The 

 mycelium from a single spore, then, is a thallus. Since two dif- 

 ferent thalli of the bread mold are necessary to bring about con- 

 jugation and produce zygospores, such a thallus plant is said to be 

 heterothallic, because other or different thalli must be brought to- 

 gether for sexual reproduction. They are also said to be dioe- 

 cious. The Mucor mucedo above mentioned is also dicecious. In 

 some of the molds there is a differene in the size of the two differ- 

 ent thalli ; the one supposed to represent the female is larger and 

 is by some indicated as + . The other being smaller is indicated 

 . By extension + and are applied to corresponding strains 

 in species where the thalli are of equal size. 



421. Monoecious Mucors.* Some of the mucors are 

 moncecious,j i.e., both sexes are present in the mycelium from 

 a single spore. This is true in the mushroom mold (Sporodinia 

 grandis), a common mold growing on decaying mushrooms in 

 the woods. 



4:22. Nature of the spores in the germ sporangium. The 

 name germ sporangium is by some applied to the spore case which 

 is formed from the germinating zygospore. Since the sexes 

 become mixed in the zygospore of the dicecious species they must 

 be separated again, otherwise the species would become monoe- 

 cious. This separation takes place in Phycomyces nitens in the 

 formation of the spores in the germ sporangia, so that there are + 



* Mucorineae, or Mucorales. The order containing different genera and 

 many species of Mucors is called Mucorinece, or Mucorales. 

 j" Homothallic, because all the thalli are alike sexually. 



