46 PLANT-LIFE 



which becomes swollen and barrel-shaped; this cell is 

 termed the " oogonium" (Gr. oon, an egg; gone, genera- 

 tion). The egg is relatively large; it bears a colourless 

 spot. In the wall of the oogonium opposite this spot 

 an opening appears, and through this opening a little of 

 the transparent protoplasm of the egg-cell is protruded. 

 The egg-cell is now ready for fertilization. The sper- 

 matozoids essential for this vital business are developed 

 in cells of the same or another thallus; they are like 

 small zoospores. The special cells in which they are 

 produced, usually two per cell, are termed " antheridia." 

 A spermatozoid swims to the egg-cell, comes in contact 

 with the protruded protoplasm, passes through the hole 

 in the oogonium, and fuses with the passive egg. The 

 fertilized egg secretes a cell- wall, and enters into a resting- 

 state, in which it may remain for a few weeks. When it 

 comes to germinate, the cell- wall is ruptured, and the 

 contents, now enclosed in a delicate membrane, escape. 

 Ordinarily the cell does not develop directly into a new 

 plant; it divides into four cells, each of which becomes 

 a zoospore similar to those produced asexually. All 

 four zoospores escape, and, after fulfilling their roving 

 commission, settle down and germinate. Thus four new 

 plants are produced from one egg. 



In some species of (Edogoniwm both sexes are 

 represented in one filament; such are said to be mon- 

 oecious. In others each sex is confined to a separate 

 filament; they are dioecious. But many species have 

 devised a rather more complicated sexual arrangement 

 than that just described: the spermatozoids are produced 

 from what are known as " dwarf males." This is the 

 story: A series of small cells, much shorter than the 



