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128 ZYGNEMATACEAE
Spore form, spore size, and wall ornamentation in hybrid
zygospores are produced by the cytoplasm of the receptive gamete.
For example, in collections containing filaments of two species
interconjugating, the spore is always similar in form and approx-
imate size to that of the specific filament in which the spore is
formed. Hybridization between a species with plane-walled spores
and a species with ornamented spore walls results in plane-walled
or ornamented zygospores, depending upon the specific filament
in which the receptive gamete is located. These facts fit in with
observations on the movements of gametes during conjugation in
which the male gamete moves into and through the cytoplasm of
the female gamete and becomes enclosed by it. Thus the surface
of the female gamete alone underlies the spore wall during its
development. This is not interpreted as cytoplasmic inheritance.
More probably the factors for these qualities of the cytoplasm are
in the chromosomes. The cytoplasm is merely the mechanism by
which spore wall forms, sizes, and patterns are formed.
The processes of gamete organization, movement, and union
usually occur during the night. To study the successive steps
through the microscope one must avoid subjecting the cells to
intense light and high temperatures during the observations.
Under these conditions the motile gametes may stop moving and
become lodged at the sides or ends of the receptive gametes. This
abnormal condition may be seen in published photographs of the
process. Observations are best made at short intervals by turning
the light on and oflf or by tilting the mirror backward and forward.
Analysis of Characteristics of the 275 Species
OF Spirogyra Here Described
Number of species with end walls plane is 208; semireplicate, 2; rep-
licate, 65.
Extreme diameters of vegetative cells with end walls plane are 10-200/1;
semireplicate, 12-18/1; replicate, 8-61 /i.
Number of chromatophores in species with end walls plane is i to 16;
semireplicate, i ; replicate, i to 4.
Number of species usually having i chromatophore is 129; approx-
imately 2 to 5 chromatophores, 109; and 6 to 16 chromatophores, 37.
Of the 208 species with plane end walls, the usual mode of conjugation
is scalariform in 166, scalariform and lateral in 26, and lateral in 10.
Conjugation is very rare or unknown in 6.