ZYGOMYCETES 



95 



usually differing slightly in physiological characters or the positive one 

 is better developed. 



Concerning the internal structure of the hypha, only a few details 

 are known; thus the hyaloplasm of Mortierella reticulata and Rhizopus 

 nigricans (Moreau, 1913) contracts into peculiar strands parallel to the 

 hyphal axis. The nuclei are very small throughout (1 to 3 ji in diameter). 

 They divide simultaneously, both directly and indirectly, in the same 

 hyphal region. The number of chromosomes is two. 



h a 



Fig. 54. — Mucor racemosus. 1. Sporangiophores. 2. Sporangium. 3. Opening sporan- 

 gium with columella and collar. 4. Yeast-like cells. 5. Hyphae with gemmae. 6, 7. 

 Sprouting cells; A-, young sprout cells. 8. Sporangiospores with growing germ tube, fcs. 

 9. Young hypha forming oidia and sprout cells. (1 X 2; 2, 3, 6 to 9 X 300; 4 X 120; 

 5 X 80; after Brefeld, Pasteur and Reess.) 



The hyphae generally spread out evenly within and upon the sub- 

 strate. Rhizopus and Absidia have more or less well-differentiated 

 stolons consisting of a node, provided with appressoria or rhizoids (Fig. 

 55, 1); from the latter radiate new stolons. The rhizoids of the forms 

 parasitic on other Mucoraceae are further modified; thus in Mortierella 

 Bainieri, they grasp the host hyphae as claws or spirals, and in Pipto- 

 cephalis Freseniana, penetrate the interior of the hypha and there branch 

 into a small tuft (Fig. 63). 



Puzzling relations have developed in Chaetocladium and Parasitella. 

 The mycelium of Chaetocladium Brejeldi var. macrosporum (Burgeff, 



