CERTAIN SPECIES OF MUCOR 303 
black, not transparent, encrusted with crystals about 2 » long; 
sporangium wall deliquescent, leaving a large or small basal 
membrane; columella free, oval, pyriform, conical, or elongated, 
mostly oval apiculate, usually with one to five spines (exception- 
ally up to twelve) at the apex, although sometimes smooth, 21-43 
< 14-25 u, brown; spores globose (a few irregular), 5-8 w (a few 
4») in diameter, dark brown; zygospores not found (species pre- 
sumably heterothallic). 
This species was collected twice: from soil in greenhouse, and 
on decayed Brazil nut. Nos. 44 and 75. It is closely related to 
Mucor plumbeus, but differs in its habit of growth (M. 
plumbeus is 1 cm. tall), smaller sporangia, larger and smooth 
spores. 
Mucor spinescens has never been found to exceed 8 mm. on 
any medium on which it has been grown and usually it is but from 
2-5 mm. tall. On levulose and on dextrin gelatin it forms a dark 
brownish gray turf 8 mm. tall. On rice the turf is chaetura black 
(Ridgway) and only 3 mm. tall, while on grapefruit the turf is 
4 mm. tall and fuscous (Ridgway). Fermentation of dextrose 
was obtained and the species is capable of slowly oxidizing 
tyrosin. 
VI. DISCUSSION 
1. TESTS FOR ZYGOSPORES 
With the single exception of Mucor proliferus, zygospores were 
not found in any cultures of the heterothallic species studied. 
This is accounted for by the fact that single spore cultures formed 
the starting point for the study of every number isolated. Con- 
sequently it was deemed necessary to test the various collections 
of the same and of closely related species for zygospore production. 
In a preliminary set glucose gelatin was used, but in the final 
experiments Blakeslee’s agar, the formula of which has been given, 
was used. Petri dishes were inoculated with four numbers of 
mucors and the cultures were examined when growth had resulted 
in a contact of the hyphae of all the four numbers. With the 
exception of Mucor spinescens, M. sphaerosporus, and Nos. 9 and 
32 (M. abundans), all of the species collected were tested. In all 
about one hundred fifty different pairs of combinations were used, 
but the results proved negative in every case. 
