xix CONJUGATION 199 



Thus, as in Mucor, the gametes are similar and equal- 

 sized, and the result of the process is a resting zygote or 

 zygospore. But while in Mucor each gamete meets the other 

 half way, so that there is absolutely no sexual differentiation, 

 in Spirogyra, as in Vaucheria, one gamete remains passive, 

 and conjugation is effected by the activity of the other. So 

 that we have here the very simplest case of sexual differen- 

 tiation : the gametes, although of equal size and similar ap- 

 pearance, are divisible into an active or male cell, correspond- 

 ing with the sperm of Vaucheria, and a passive or female 

 cell corresponding with the ovum. It will be seen that in 

 Spirogyra the whole of the protoplasm of each gonad is used 

 up in the formation of a single gamete, whereas in Vaucheria, 

 while this is the case with the ovary, numerous gametes 

 (sperms) are formed from the protoplasm of the spermary. 



In some forms of Spirogyra conjugation takes place not 

 between opposite cells of distinct filaments, but between 

 adjacent cells of the same filament. Each of the gonads 

 sends out a short process (D 1 , a) which abuts against a 

 corresponding process from the adjoining cell : the two 

 processes are placed in communication with one another by 

 a small aperture (o 2 ) through which the male gamete makes 

 its way in order to conjugate with the female gamete and 

 form a zygote (zyg). 



In the ordinary ladder-like method of conjugation the 

 conjugating filaments appear to be of opposite sexes, one 

 producing only male, the other only female gametes : the plant 

 in this case is said to be dioecious, i.e., has the sexes lodged in 

 distinct individuals, and conjugation is a process of cross- 

 fertilization. But in the method described in the preceding 

 paragraph the individual filaments are monoecious, i.e., produce 

 both male and female cells, and conjugation is a process of 

 self-fertilization. 



