SPIROGYRA. 



6 9 



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 -plasmoly zed 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 



FIG. 20. Fusion of gametes in Spirogyra. 



A, portion of two conjugating filaments of Spirogyra yufnina. (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 Spirogyra heeriana^ 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 



See Fig. 10, p. 17, Die Naturlichen Pflanzenfamilien, i Theil, 2 Abtheilung. 



