CONJUGATE. 



45 



The conjugation among the Zygnemacese takes place in the 

 following manner : the cells of two filaments, lying side by side, or 



A B 



FIG. 39. Spirogyra longata. A At the commencement of conjugation, the conjugation- 

 canals begin to protrude at a and touch one another at b ; the spiral chlorophyll band and 

 cell-nuclei (fc) are shown. B A more advanced stage of conjugation; a, a' the rounded 

 female and male aplanogametes : in b' the male aplanogamete is going over to and 

 uniting with the female aplanogamete (b). 



two cells, the one being situated above the other in the same fila- 

 ment (Fig. 41), push out small protuberances opposite each other 

 (Fig. 39 A, a, 6) ; these finally meet, and the dividing wall is ab- 

 sorbed so that a tube is formed connecting one cell with the other; 



FIG. 40. A cell of Zygnema. S Pyrenoid. 



FIG. 41. Zygnema insigne, with zygote. 



the protoplasmic contents round off, and the whole of these contents 

 of one of the cells glides through the conjugation-tube and coalesces 



with that of the 

 other (Fig. 39 B\ 

 the aggregate mass 

 then rounds off, sur- 

 rounds itself with 



FIG. 42. Germinating zygote of Spirogyra jugalis : the a Cell-Wall, and be- 

 .young plant is still unicellular ; the end which is still in 

 the wall of the zygote is elongated and root-like; tho 

 chromatophore divides and forms the spiral band. 



comes a zygote. A 

 distinct difference 



