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MOUGEOTIA 8i
not be cited as proof that the aplanospores so commonly found
among the Mougeotias are the result of lateral conjugation.
Two unusual growth processes occur among several species of
Mougeotia, of which M. genuflexa and M. reinschii are the commonest
examples; these are adhesion and genuflexion. It is true
that as new filaments appear in some permanent ponds, new
adhesions and genuflexions may continue to develop for several
successive months. Apparently cells coming in contact produce
growth substances which cause pectinization of the walls in contact
and increased growth of the wall at the point of contact. The
first results in adhesion; the second in genuflexion.
Genuflexion is not an early stage in conjugation that has been
terminated before the development of tubes. There is no evidence
that it has either an advantage or a purpose, although various
authors have sought to find one. In one pond in which the process
occurred throughout the growing season during several successive
years, the interlocked filaments survived for a short time and then
fragmented and went to the bottom. No zygospores were ever
collected from this pond during the six years of observation.
The steps in conjugation in the Mougeotias as in the other
genera in this family are probably activated in the same manner
as those observed by J. R. Raper in Achlya {Amer. Jour. Bot.
[1939-40]), a fungus in which the succession of hormones seems
to have been established clearly.
Analogous changes occur in sexual reproduction though the
cells are not necessarily in contact. The first visible changes are
the growth of two papillae from nearby cells, until they meet,
adhere, and the walls in contact are dissolved. Possibly other
hormones lead to the movement of the protoplasts of both gam-
etangia into the conjugating tube, which meanwhile has greatly
enlarged, and growth has resulted in a form characteristic of the
species. Then follows the union of gametes and the deposition
of successive layers of the spore wall.
With a few exceptions zygospores and aplanospores of Mou-
geotia have only two walls—an outer chitinous wall variously
colored and ornamented, and an inner transparent wall. In many
species the spores are enclosed by a sporangium wall, in others
the sporangium is merely a combination of gametangial and tube
walls. In some species the outer layer of the sporangium wall
changes to pectic compounds and forms a transparent layer 2 to