l62 SAPROPHYTIC FUNGI 



and bacterial colonies starting on a given surface of 

 sterilised nutritive agar or gelatine which has been 

 exposed to the air for a given time. 



(2) Chlamydospore formation. — In some species of 

 Mucor the protoplasm may contract into oval masses 

 at short intervals along the length of a hypha (for 

 instance a sporangiophore) the short diameter of the 

 oval corresponding with or shghtly exceeding the 

 width of the hypha. Each oval mass becomes clothed 

 with an independent thick wall, which often bulges 

 out the walls of the parent hypha. The chlamy do- 

 spores so produced become free by the breaking 

 up of the wall of the now empty hypha, and are 

 resistant resting spores which germinate to produce 

 new plants under favourable conditions. Similar 

 chlamydospore formation is not uncommon among 

 fungi. 



(3) Conjugation. — Quite a different sort of repro- 

 ductive process sometimes occurs in Mucor. The tips 

 of two hyphse arising from the same or from different 

 branches of the mycelium approach one another, and 

 come into contact (Fig. 16, e), each swelling into the 

 form of a club. A cross wall is formed towards the 

 base of each club-shaped structure, cutting off a com- 

 partment at the tip (Fig. 16, /). One of these is fre- 

 quently larger and more swollen than the other. The 

 walls at the tips which are in contact are now 

 absorbed and the cytoplasm of the two compart- 

 ments mingles. The nuclei divide actively and then 

 conjugate in pairs. The walls now swell up, forming 

 a nearly spherical structure, and become dark-coloured, 

 often black, with projecting excrescences on the sur- 

 face (Fig. 16, h). Eventually the zygote (product of 

 conjugation so formed) separates from the hyphas on 



