THE THALLOPHYTES 353 
sporangia (spore cases) arise, which are unicellular. They con- 
tain numerous biciliate zodspores, which escape into the sea water, 
move about and later develop into new Ectocarpus plants. Along 
the filaments several branches will be seen. Some of these have 
undergone division into several cells and these again into still 
smaller cells until many-celled chambers have resulted, which are 
called plurilocular gametangia. Each cell of a_ plurilocular 
Fic. 257.—Ectocarpus siliculosus, a filamentous brown alga. A. Unicellular 
sporangia, one containing zodspores, the other empty; z, a zodspore. 8B. Pluri- 
locular gameangia, the larger mature, the smaller still showing the outlines of the 
original cells in the branch from which it arose. C, Union of two gametes to form 
the zygospore.—C, after Oltmanns. (From Bergen and Davis Principles of Botany.) 
gametangium contains a gamete or sexual cell, which resembles 
in many details a zoéspore. When the gametangium matures 
these gametes are discharged into the salt water. They fuse 
together in pairs and form zpgospores. Each zygospore under- 
goes a resting stage and upon the advent of favorable conditions 
develops into a new Ectocarpus filament. 
Tue Keips.—To this group (Order Laminariales) belong the 
largest living representatives of the Alga. _ They are represented 
