266 
THALLOPHYTES. 
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 Mucor-yQ.<ist 
(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. \q<^.—PiptocephaHs Freseniana (after Brefeld). M a piece of the 
mycelium of Mucor Mucedo from which the mycelium of Piptocephalis m m 
derives its nutriment ; h the haustoria of Piptocephalis 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 mycelium ; 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. 
