492 Harper . — Cell- Division in Sporangia and Asci. 
partially sterilized by repeated exposure to the temperature 
of boiling water, with spores from a culture which has appeared 
spontaneously. The sporangia can be caught on a clean 
slide as they are thrown off, and the spores are sufficiently 
free from bacteria when simply rubbed in a drop of water 
to use in infecting the partially sterilized dung. The culture 
can conveniently be made in a crystallizing dish of any size. 
In seven or eight days the sporangiophores begin to appear. 
Successive crops of sporangia are matured for several days, 
and thus abundant opportunity is given to secure any desired 
amount of material at any stage in development. The spo- 
rangiophores stand in dense turfs, . completely covering the 
surface of the substratum. Not the least favourable feature 
of this fungus for cytological study is the exact regularity 
with which the different stages succeed each other through 
the day and night. The well-known yellow bulb-like swellings 
of the mycelium from which the sporangiophores arise appear 
in abundance on the dung in the early afternoon. This is 
a favourable period for studying nuclear division in this fungus. 
The vegetative nuclei in these bulbs divide rapidly to form 
the numerous nuclei which are afterwards cut off in the 
sporangium to form the spores. A little later the sporangio- 
phores bud out from the bulblets and grow toward the light. 
Late in the afternoon the ends of the sporangiophores begin 
to swell to form the sporanges. The columella wall is formed 
about midnight. Segmentation occurs between one and four 
o’clock a.m. Embryonic development of the spores goes 
on from four to seven, and the ripe sporanges will be thrown 
off from nine till twelve a.m. The whole process is repeated 
at approximately the same daily periods for three or four 
days, when the culture is exhausted. The above periods of 
course vary somewhat with differences in temperature, moisture, 
&c., and the development of different sporangia is also not 
exactly parallel. Still, material fixed at the periods men- 
tioned has always shown in my experience the majority of 
the sporangia in the stages noted. The general facts as to 
the development of Pilobolus have been very well worked out 
