196 



STRUCTURAL BOTANY 



however, divide into two cells only (see Fig. 85) by a 

 transverse wall. Each of the two daughter-cells has one 

 central nucleus ; the remaining six nuclei are expelled 

 from the ova, together with a little protoplasm. The 

 bodies seen close to the transverse septum in Fig. 86, A, 

 are some of these rejected nuclei. In Fucus itself all the 



FIG. 84. Spermatozoids of Pelvetia. A, unripe antheridium, 

 already freed from outer membrane ; JS, antheridium open- 

 ing to emit the biciliate spermatozoids (sp) ; c, c, empty mem- 

 branes. Magnified about 450. (After Thuret and Bornet. ) 



eight nuclei are utilised, for the oogonium there divides 

 into eight cells ; in another genus (Ascophyllum) four cells 

 are formed and four nuclei rejected, while in the majority 

 of the family no division of the cell contents takes place, 

 and of the eight nuclei formed in the oogonium only one 

 serves as the functional nucleus of the ovum. 1 



1 The fact that a number of nuclei are always formed suggests that the 

 oogonium of Fucaceee was originally a structure of the nature of a 

 sporangium. 



