246 
PLANT STUDIES 
be solitary or several in a cell, and form very striking and 
conspicuous objects (Figs. 212, 213). 
Spirogyra and its associates are further peculiar in pro- 
ducing no asexual spores, and also in the method of sexual 
reproduction. Two adjacent filaments put out tubular 
processes toward one another. A cell of one filament sends 
out a process which seeks to meet a corresponding process 
from a cell of the other filament. When the tips of two 
such processes come together, the end walls disappear, 
FIG. 214. Spirogyra, showing some common exceptions. At A two cells have been 
connected by a tube, but without fusion a zygote has been organized in each cell; 
also, the upper cell to the left has attempted to conjugate with the cell to the 
right. At B there are cells from three filaments, the cells of the central one hav- 
ing conjugated with both of the others. CALDWELL. 
and a continuous tube extending between the two cells is 
organized (Figs. 213, 214). When many of the cells of two 
parallel filaments become thus united, the appearance is 
that of a ladder, with the filaments as the side pieces, and 
the connecting tubes as the rounds. 
While the connecting tube is being developed the con- 
tents of the two cells are organizing, and after the comple- 
tion of the tube the contents of one cell pass through and 
enter the other cell, fuse with its contents, and a sexual 
