DROWN ALGAE 



387 



its attractive influence on their movements (Fig. 287, 5). But only 

 one penetrates each egg, and its nucleus has been followed on its 

 course through the cytoplasm till it fuses with the nucleus of the 

 ovum (Fig. 287, 6). The rest at once move away, as though a repellent 

 influence from the egg had replaced the previous attraction. 



The immediate consequence of fertilisation is the deposit of a 

 cell-wall covering the zygote. It settles on some solid substratum, 



Fig. 289. 



I.-IV. Drawings direct from successively older plants of Fucus serratus, showing 



the regular dichotomy. 



and germinates directly into a new Fucus plant. Stones on a rocky 

 shore where Fucoids grow may be found in summer covered by a 

 dense growth of myriads of these young plants (Fig. 289). 



In the life-history of Fucus the increase in numbers is exclusively through 

 the sexual process. There is no production of zoospores, nor any non-sexual 

 propagation, as there is in the simpler Brown Seaweeds. The Fucus plant is 

 diploid and reduction takes place in the first divisions respectively of the 

 antheridial and oogonial cells. The haploid phase is extremely brief and there 

 is, strictly speaking, no alternation of generations as in Laminaria. By com- 

 parison with the very reduced gametophyte of Laminaria, it has been suggested 



