266 



THALLOPHVTES. 



a different kind, the filaments breaking up by the formation of septa into short 

 segments, which then become rounded off, and are able, under favourable conditions, 

 to produce new mycelium. This explains the production of the so-called iWwcor-yeast 

 (from Mucor racemosus'^), which bears a striking resemblance to true yeast {Saccharo- 

 myces) ; the mycelial gonidia can multiply by a yeast-like budding when placed in 

 an unsuitable nutrient fluid. 



The mycelium has the power, under special circumstances, of reaching the mor- 

 phological completion of its development by the formation of sexual reproductive organs. 

 Thicker branchlets with a club-shaped extremity are produced on neighbouring filaments 



Fig. \^<,.—P^ptocephalis Freseniana (after Brefeld). M a piece of the 

 mycelium of Mucor Mucedo from which the mycelium of Piptocephaiis tn m 

 derives its nutriment ; h the haustoria of Piptocephaiis which penetrate the 

 mycelial filaments of Mucor; c a conidiophore ; ss the two conjugating 

 branches of the mycelium which give rise to the zygospore Z. 



of the mycehum ; the apices of these branchlets come into contact, and coalesce by the 

 disappearance of the cell-walls at the point where they touch (Fig. 174 D and 175 Z; 

 see also 162 B) after a septum has been formed in each filament on each side of 

 the point of conjugation. The protoplasm collects in the space which has been 

 thus marked off; and a zygospore of comparatively large size is produced by the 

 growth either of the entire space thus separated (Fig. 174 C) or of its central part 

 only (Fig. 175 Z) ; the thick outer wall of the zygospore being usually of a dark 

 colour and furnished with protuberances or spiny outgrowths. The zygospore ger- 



^ Brefeld, Flora, 1873, no. 25. 



