FUCUS 99 



. Does a plant of Fucus vesiculosus have both sexual organs 

 in the same conceptacle ? on the same plant ? Draw : 



1. The female organs, oogonia, large cells which develop 

 eight eggs each. 



2. The male organs, antheridia, small cells generally borne 

 in clusters on stalks. Each develops numerous (over one 

 hundred) sperms. 



Because of the extreme differentiation of the eggs and sperms 

 the condition in Fucus is one of the highest expressions of het- 

 erogamy. 



A plant is called dioecious when the sexual organs are borne on 

 different individuals, moncecious if both organs are on the same 

 individual. 



D. Cut tMn sections in pith or study stained microtome sections of recep- 

 tacles (Sec. 212) and draw on a large scale the outline of a conceptacle, 

 showing the opening with protruding filaments, paraphyses, the lining 

 membrane with the sexual organs in position, the network of filaments 

 within the receptacle. 



E. Living male and female plants may be separated, rolled up in paper, ■ 

 and kept in a tight box. The contents of ripe conceptacles will then 

 ooze out from the openings. When such contents are placed in sea 

 water the slime dissolves and the gametes, eggs or sperms, are set free. 

 If mixed together the sperms at once swarm around the eggs and the 

 conditions under which fertilization takes place may be observed 

 under the microscope. Note the rotation of the eggs, set in motion by 

 the swarming of the sperms. Sketch the appearance of the eggs. Stain 

 with iodine and draw the sperms under the highest magnification. 



F. Fertilized eggs if placed in sea water in a covered watch glass will 

 germinate, developing into sporelings. Draw stages. 



Questions. Where do the rockweeds grow? How can they 

 withstand the beating of surf on the rocks? Would the 

 vegetative body of a rockweed be called a thallus ? Why ? 

 Of what service are the air bladders ? Where does fertiliza- 

 tion take place in nature. How might the gametes escape 

 from the conceptacles ? Why is it not necessary for an 

 egg to become a resting spore (oospore) in a marine alga ? 

 Describe the life history of Fucus. 



