240 



GENERAL BOTANY 



numbers around them, probably attracted by a secretion from 

 the female gamete. When one male gamete has succeeded in 

 penetrating the outer cytoplasmic layer of the female gamete, 

 the other swarming male gametes either disappear or die in con- 

 tact with the egg. Cytoplasmic and nuclear fusions complete 



the act of fertilization, and the 

 fertilized egg becomes the zy- 

 gote, which quickly secretes 

 a cellulose wall and begins to 

 divide to form a new Fucus 

 offspring (Fig. 129 d, e). 



Germination of the zygote 

 follows immediately upon the 

 fertilizing act instead of after 

 a long rest period as in Spi- 

 rogyra and most fresh-water 

 algae. This early germination 

 of the zygote is undoubtedly 

 connected with the fact that 

 Fucus lives in the sea, where 

 the danger of extermination in 

 winter or in dry periods is 

 much less than in fresh-water 



FIG. 129. Development of the male 

 gametes, fertilization, and develop- 

 ment of the embryo in Fucus 



a, antheridium with sperm mother cells ; ponds and lakes. Winter is 



6, expulsion of free sperms ; c. swarming , -, ^ /. n . , -, 



of sperms around an egg preparatory thus P assed safel y m the 



to fertilization ; d, the cellular embryo ; vegetative condition, and the 



e, more advanced embryo of Fucus. i 11 , i , 



After Thuret highly protected resting zygote 



is not a necessity in its life 



cycle. Germination of the zygote results in a many-celled 

 embryo, which differentiates to form a growing point and a 

 holdfast by which the young offspring becomes anchored to a 

 stone or other object. Elongation and repeated forking of the 

 original growing point follows, which finally results in a new 

 offspring like the parent. 



Life history. The life history of Fucus does not differ materially 

 from that of Spirogyra except in the fact that no resting zygote 

 is formed to tide over inclement periods. Asexual reproduction is 



