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 fertilized 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 Fucaceae (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 fertilization. Soon 
after fertilization the oosperm or zygote becomes sur- 
rounded by a delicate 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 fertilization 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 have become 
attached to its surface. By the vigorous lashing of their 
cilia 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 
