1202 Wisconsin Academy of Sciences, Arts, and Letters. 
The spore differentiation begins at this time. The vacuoles 
lose their rounded form and become angular. As the edges or 
points of the vacuoles come in contact, they unite, forming 
clefts in the plasm. Furrows cut into the sporeplasm from the 
columella. These unite with the clefts formed by the vacuoles 
and cut the plasm into irregular masses. The spores vary in 
size and in the number of nuclei. The nuclei remain in the 
resting stage throughout this process; no cases of nuclear di¬ 
visions were observed by Swingle. 
All the cytoplasm and the nuclei are included in the spores 
themselves. Between the spores there occurs the intersporal 
slime which has originated in the vacuoles and which Swingle 
believes arises as a secretion from the vacuolar membrane. It 
is homogeneous when the spores are formed, stains a bluish 
brown with the triple stain, and contains no nuclei or other in¬ 
clusions. 
The columella wall begins to form while the spore cleavage 
is going on and continues to thicken until the spores are ripe. 
Thus it has been shown in this form, as well as by Harper 
(1899) for Pilobolus and Sporodinia, that the columella wall 
arises as a dome-shaped structure from the very first and not 
as a straight wall which later arches up, as has been so erron¬ 
eously described in many places. The spores finally become 
invested with a refringent cell wall which is very resistant to 
stains. 
Studies of the plus and minus sporangia were made in order 
to determine whether or not any morphological differences exist 
between the two strains. The sporangia of the two strains 
are structurally alike as far as it has been possible to determine. 
The young sporangiophores of both show a marked increase in 
the number of nuclei. The nuclei, to all appearances, are sim¬ 
ilar. The subsequent changes that take place in the formation 
of the columella and production of spores proceed alike in the 
two strains. 
The character of the growth of the plus and minus strains 
is unlike, and when cultures of each are grown side by side it 
is possible to distinguish between them. The mycelium in the 
minus strain grows somewhat more slowly and less vigorously 
and the sporangia appear to be fewer and later in appearance. 
