Keene—Studies in Zygospore Formation. 1201 
The spores germinate readily in water or various weak sugar 
solutions and broths. They enlarge somewhat and one or two 
germ tubes push out (Pl. II, fig. 8). These grow for some dis¬ 
tance during which time the number of nuclei present increases. 
Careful studies have revealed no differences between the spores 
of the two strains. The germ tube branches and sub-branches 
forming the hyphal network over and through the substratum. 
At intervals characteristic enlargements occur and occasionally 
from these, rhizoid-like branches grow out. In other cases, 
however, these enlargements appear merely as swellings and 
what they are functionally remains a question. Internally they 
appear much as any other portion of the mycelium; sometimes 
there occurs a clustering of the nuclei in this region. The small 
sporangia which are formed first and are produced close to 
the substratum appear to be typical in formation and produc¬ 
tion of spores. The aerial branches which are destined to form 
the large sporangia appear yellowish with a blackening toward 
the base. The yellow color is due to the presence of a large 
amount of oil, as shown by tests, which exudes in droplets when 
the sporangiophores are crushed. As the sporangiophores 
elongate they exhibit an extreme sensitiveness to light, the ter¬ 
minal portions bending toward the source of illumination. If 
grown in the dark, they elongate to a greater extent than when 
grown in the light. 
The history of the formation of the sporangia and of the 
origin of the spores has been worked out by Swingle (1903). 
The young sporangiophores are densely crowded with cytoplasm 
and nuclei. The tip swells out into a small rounded structure. 
The contents of this are evenly distributed at first but later a 
zonation appears with the denser portion of the protoplasm 
toward the periphery and the vacuolate portion at the center. 
There occurs a marked streaming of the protoplasm into the 
sporangium at this stage and the rounded vacuoles of the cen¬ 
tral portion move out to the periphery. They become filled 
with stainable contents which appear bluish when the triple 
stain is used. The nuclei are at first evenly distributed through 
the outer zone, few occurring in the central region. A layer 
of vacuoles having stainable contents becomes arranged in a 
dome-shape in the denser portion. The vacuoles flatten, fuse 
edge to edge and form a continuous cleft which is filled with 
the same material that filled the vacuoles. 
76— S. A. L. 
