i8o 



MORPHOLOGY. 



thread of the mycelium. In other cases large portions of the threads of the 

 mycelium may separate into chains of cells. Both these kinds of cells are 



Fig. 194. 



A mucor (Rhizopus nigricans) ; at left nearly mature sporangium with columella showing 

 within; in the middle is ruptured sporangium with some of the gonidia clinging to the colu- 

 mella ; at right two ruptured sporangia with everted columella. 



capable of growing and forming the mycelium again. They are sometimes 

 called chlamydospores. 



890a. The Mucorinese according to their manner of zygospore formation 

 are of two kindst ist, the homothalftc (monoecious), in which all of the colo- 

 nies 01 thalli developed from different spores are the same, and both gametes 

 may be developed from the mycelium from a single spore, as in Sporodinia 

 grandis, a mould common on old mushrooms; ad, the heterothallic (dioe- 

 cious), in which certain plants are of a male nature and small in compari- 

 son with those of perhaps a female nature which are larger or more vigor- 

 ous. When grown separately each of these two kinds of thalli, or colonies 

 of mycelium, produce their own kind but only sporangia. If the two kinds 

 are brought together, however, branches from one conjugate with branches 

 from the other and zygospores are produced, as in Rhizopus nigricans, the 

 common bread or fruit mould. This is one reason why we rarely find this 

 fungus forming zygospores. (See Blakeslee, Sexual Reproduction in the 

 Mucorineae, Proc. Am. Acad. Arts and Sci., 40, 205-319, pi. 1-4, 1904.) 



