The Algae 453 



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 oogonium and unites 

 with the egg. The egg and the sperm may be of the same 

 filament or of different filaments. The product is an oospore 

 (egg spore). After a dormant period this produces four swim- 

 ming 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, swimming cell that 

 moves to the egg and accomplishes fertilization by uniting with 

 it. The product is an oospore which germinates and produces 

 four swimming spores. These start a new generation of the 

 filamentous plants. 



Reproduction among the algae. The methods of reproduction 

 among the algae that we have studied are representative of those 

 found in the entire group. The three general types are : 



(i) Vegetative multiplication. By means of cell division all 

 masses, filaments, or highly branched plant bodies are produced. 

 If the individual cells separate from each other after division,' 

 as in Protococcus, many new individual plants are produced ; 

 and when filaments and branched forms are broken, as in Mi- 

 crospora, a new individual plant is produced by each part. 



(2) Reproduction by spores. Vegetative cells form thick- 

 walled resting spores which carry the plant over to the next 

 season. Another kind of spore is the swimming spore, by means 

 of which the plant secures immediate reproduction and spreads 

 to other parts of the pond or stream. These spores are formed 

 directly from vegetative cells, or by the division of vegetative 

 cells. There is no union of cells as there is when sexual spores 

 are formed. 



