336 A TEXTBOOK OF GENERAL BOTANY 
filament (Fig. 346). When the projections from opposite cells 
come into contact, the walls between them are absorbed so that a 
tube connects a cell of one filament’with a cell of the opposite 

Fig. 347. Conjugation of Spirogyra 
Successive stages in conjugation ina species 
in which conjugation is between two neigh- 
boring cells ; the last figure shows mature 
zygospore. (x 200) 
filament. The protoplasm of 
one cell then moves through 
the tube into the opposite 
cell and fuses with the pro- 
toplasm of that cell. Usually 
all the cells of a filament be- 
have alike in sexual fusion ; 
for example, if one cell of 
a filament retains its con- 
tents and receives the proto- 
plasm from the opposite cell, 
all cells in the same fila- 
ment do lkewise. 
If the filaments having 
only receiving cells can be 
considered as indicating a 
female condition, Spirogyra 
shows what may be regarded 
as a very shght differentia- 
tion of sexes. 
The fusion of the proto- 
plasm of two cells results in 
the formation of a zygospore, 
which surrounds itself with 
a thick cell wall (Fig. 346). 
The zygospores can with- 
stand adverse conditions: 
for instance, the ordinary vegetative cells of Spirogyra would 
be killed quickly by drying, but the zygospores can withstand 
prolonged periods of drying. In consequence of this fact they 
can be transported from one body of water to another, or, 
when the water in a pool dries up, they can survive until they 
are again surrounded by water. 
