SPIROGYRA. 69 
gamete, which passes through the canal to unite with the stationary or 
female gamete (Fig. 20, A). Strasburger (’78) has observed that 
occasionally the female cell was the first to round up. Haberlandt 
suggests that the extrusion of water is connected with a mutual 
stimulus between the cells, for the female gamete contracted only 
when the male was normal, and, furthermore, the male cell became 
self-plasmolyzed only when connected with a female cell. 
The principle underlying the movement of the male gamete through 
the canal is not well understood. Overton (’88) held that a gelatin- 
ous substance was secreted, which, upon swelling, forced the proto- 
plast through the canal. The presence of a mucilaginous substance 
Fic. 20.—Fusion of gametes in Spzrogyra. 
A, portion of two conjugating filaments of Spirogyra guinina,—(After 
Strasburger.). 
B, young zygote provided with only a thin wall, 
C, zygote at a later stage; the cell-wall is thicker, and the nuclei have 
united, but the nucleoli have not fused. 
has not been demonstrated, however, and it is highly probable that we 
have to do here with an active plasmic movement operating under the 
chemotactic stimulus of the two protoplasts. Here fecundation con- 
sists in the union of the entire plasma of both gametes, though DeBary 
records the case of Sférogyra heertana' in which a small vesicle of 
plasma is left beyond the partition wall in the conjugation canal. 
Concerning the behavior of the chlorophyll bands in the zygote, 
much diversity of opinion exists. DeBary (’58) and Schmitz (’82) 
observed that in species with one chlorophyll band the two chloro- 
plasts united in the zygote to form one continuous band. Overton 
(88), on the contrary, asserts that the single band of the female gamete 
segments at the middle during the fusion of the protoplasts; the two 
halves then separate, and each piece unites with the ends of the band 
1 See Fig. 10, p. 17, Die Natiirlichen Pflanzenfamilien, 1 Theil, 2 Abtheilung. 
