234 STRUCTURE AND LIFE HISTORIES 



Ascophyllum all except four (or the exceptional three or 

 five) fail to organize daughter-cells about themselves, and 

 abort. Forms having the full complement of eight eggs, 

 are, therefore, considered more primitive than those with a 

 less number. 



215. Fertilization. — The eggs are never fertihzed while 

 in the oogonia, nor even while in the conceptacle. The 

 walls of the oogonium burst, and the eggs pass out into the 

 surrounding water. They are covered with a thick layer 

 of mucilaginous substance, and by means of some material, 

 not definitely known, they attract the sperms that happen 

 to have been discharged at the same time and near the 

 same place. No other case is known in plants where the 

 difference in size between egg and sperm is so great as in 

 the Fucacese (Fig. 175). The sperms swarm about an egg, 

 and finally one of them enters it and its nucleus unites 

 with that of the egg, thus completing fertihzation. Soon 

 after fertilization the oosperm or zygote becomes sur- 

 rounded by a dehcate cellulose wall, the fertilization- 

 membrane. The setting free of the egg before fertilization 

 marks a lower stage of development than is found in the 

 mosses and ferns. 



The process of fertihzation in Fucus may be easily 

 observed by placing mature eggs and sperms together in 

 sea-water in a watch glass, under the microscope. The 

 sperms, attracted by the chemical stimulus of the sub- 

 stance excreted by the egg, swim toward it, and within 

 about five minutes large numbers of them haveTbecome 

 attached to its surface. By the vigorous lashing of their 

 ciha the egg is set in vigorous motion. One of the sperms 

 succeeds in penetrating the cytoplasm of the egg, and 

 reaches its nucleus. The fusion of the two nuclei may 



