68 FECUNDATION; NON-MOTILE ISOGAMETES. 
least, as a colony of individuals. Any cell of a filament, save those 
mentioned, may function as a gamete. 
In sexual reproduction cells of two filaments lying close side by side 
send out protuberances toward each other which meet end to end. In 
the contiguous membranes a circular opening is made by the dissolu- 
tion of the cellulose walls, through the agency of an enzyme, whereby 
a continuous canal is formed between the cells (Fig. 20, A). It is 
highly probable that the conjugating tubes are brought together by the 
aid of a chemotactic, directive stimulus. Haberlandt (’g90) claims, and 
his view is shared by Klebs (’96), that the conjugating cells exert a 
mutual chemical influence upon each other, namely, that a cell will 
put out a conjugating tube only when influenced by another, probably 
of a different sex, lying near it. In support of this view, Klebs found 
that cells of individual filaments cultivated upon agar-gelatin, although 
having been brought side by side by the folding of the filament, never 
put out conjugating protuberances. A single male filament, on the 
contrary, may conjugate with several female filaments whenever their 
cells lie sufficiently near one another, but all those cells of the male 
filament separated some distance from those of the female remain 
sterile in spite of the tendency to conjugate. The limits of this mutual 
action of the filaments (Haberlandt, ’90) is equal to.a distance of two 
or three diameters of their cells. Slightly beyond this limit the cells 
may put out short conjugating tubes, but these never reach each other, 
the stimulus being presumably too weak. Haberlandt states further that 
the conjugating tubes are not laid down simultaneously, but rather one 
sends out a protuberance which calls forth the development of the cor- 
responding tube from the other cell. If the protuberances do not lie 
exactly opposite, they bend slightly in order to meet each other. A 
further action of the stimulus is seen when a long male cetl copulates 
with two female cells. Two canals are formed connecting the male 
with the two female cells, but, of course, only one of the latter receives 
the gamete. In some species, especially Spzrogyra inflata, according 
to Klebs, the meeting of the conjugating protuberances is facilitated 
by a curving or a knee-like bending of the cells, from whose convex 
sides the protuberances arise. 
These phenomena are not presented in this connection for the purpose 
of discussing any special phase of the physiology of the sexual process, 
but merely to indicate a few features manifested by unisexual elements 
which show a tolerably well-marked tendency toward bisexuality. 
When the conjugation canal, joining the gametes, is complete, the 
turgor in each cell is diminished, so that each protoplast experiences a 
self-plasmolysis, The contraction usually takes place first in the male 
