In Closterium, of which several species have been noticed in a
conjugated state, the process appears to be nearly the same as in the
Conjugatai. Two fronds unite by means of projections arising at the
junction of the two segments, and then the newly-formed portion
continues to enlarge until the original segments are separated by a
cell of an irregular four-sided figure. The contents of the fronds,
being collected in this cell, become a dense seed-like mass, which is
sometimes globular resembling the sporangium in Mougeotia, and
sometimes square like that in Staurospermum. The newly-formed cell
is thinner and generally paler than the segments of the frond ; in some
species it looks like a prolongation of the segments, and in others these
are so loosely attached that their connection is scarcely perceptible.