242 Science of Plant Life 



found free in ponds and stagnant pools. From the cylindrical 

 vegetative cells, large swimming spores are formed. Gametes 

 also are produced. These are of two distinct forms, male 

 and female. Plants belonging to the (Edogonium group may 

 be used to exemplify reproduction in many other algaj, whose 

 gametes are essentially like those of more complex plants. 



At the time of production of the gametes, some of the cells 

 in the filament enlarge, become rounded, and accumulate 

 starch and other food material ; also, a small opening is formed 

 in the cell wall. The content of this cell is the female gamete 

 or egg, which like other eggs has in it a store of food. 



Other cells of the filament are cut up into very short cells 

 by the formation of transverse walls. In each of these short 

 cells there are formed two small gametes, which escape from 

 the filament and swim out into the water. These are the 

 male gametes, or sperms. Fertilization. takes place when one 

 of the sperms enters through the opening in the cell wall that 

 surrounds an egg and unites with the egg. The egg and the 

 sperm may be of the same filament or of different filaments. 

 The product is a sexual spore, usually called an oospore (egg 

 spore). After a dormant period this produces swimming 

 spores that start new filaments. 



In (Edogonium, therefore, the sex cells are of two kinds 

 quite distinct in structure and function. The egg is a large, 

 stationary cell filled with food. The sperm is a small, swim- 

 ming cell that moves to the egg and accomplishes fertilization 

 by uniting with it. The product is an oospore which may 

 start a new generation of plants like that which produced it. 

 This condition is essentially like that in the seed plant, where 

 the egg is produced inside a complex structure called the 

 ovule and the sperm reaches it through a pollen tube (page 



