CONJUGATION IN SPIROGYRA 



97 



behind. The chloroplastid breaks up ; the primordial utricle 



retreats from the cell-wall towards the middle, and the entire 



protoplasmic contents round themselves off into a compact 



nucleated mass -the gamete (yam.). The time has now arrived 



for the all-important event ; the gamete from one cell-chamber 



creeps through the canal into the other chamber and conjugates 



with the gamete which there awaits 



it (Fig. 44, <?.). The result is a 



zygote or zygospore (Figs. 43, 44, 



ziffj.} which surrounds itself with a 



thick protective envelope within 



the cell-wall of the parent and 



after a period of rest germinates, 



giving rise by repeated transverse 



division to a new filament. 



In this case it will be observed 

 that the two conjugating gametes 

 are morphologically alike, and we 

 may therefore describe the process 

 of conjugation as isogamous. As in 

 the case of Bodo, however, there is 

 a physiological distinction between 

 the two as regards their activity ; 

 the gamete which takes the lead 

 throughout the whole process and 

 finally crawls through the canal of 

 communication is obviously to be 

 regarded as male, and its partner 

 as female. Moreover, one entire 

 filament may produce nothing but 

 male gametes and may therefore 

 be regarded as a male plant (Fig. 

 44, $ ), while the other may produce 

 only female gametes and therefore be regarded as a female plant 

 (Fig. 44, ? ). In the closely related form, Zygogonium, there is 

 no distinction of any kind between the two sexes, both gametes 

 exhibit the same degree of activity and they meet each other half- 

 way, in the connecting canal between their respective chambers, 

 to form the zygote. 



In Spirogyra, as we have just seen, every cell of the adult plant 

 is a potential gamete or germ cell ; in the case of Volvox, it will 



B. II 



FIG. 44. Diagram of two con- 

 jugating filaments of Spiro- 



a. e., pairs of cells in successive 

 stages of conjugation ; gam., 

 male gametes; <gam. y female 

 gametes ; S.C., solitary cell ; 



