The Algae 243 



205). When the two unite in fertiHzation, the product in a 

 seed plant also is an oospore, or unfertilized egg, which im- 

 mediately divides and forms the embryo within the seed. 



Reproduction among the algae. The methods of repro- 

 duction among the algx^ that we have studied are representa- 

 tive of those found in the entire group. The three general 

 types are : 



(i) Vegetative multiplication. By means of cell division 

 cell 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 Microspora, a new individual plant is produced 

 by each part. 



(2) Reproduction by asexual spores. Vegetative cells form 

 thick-walled resting spores which carry the plant over to the 

 next season. Another kind of asexual spore is the swimming 

 spore, by means of which the plant secures immediate repro- 

 duction 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. 



(3) Sexual reproduction. A sexual spore, or oospore, is 

 formed by the union of two gametes. The gametes may be 

 similar in size and appearance, as in Ulothrix, or they may be 

 unlike, as in CEdogonium, where one gamete accumulates a 

 large food supply and the other is small and motile. In either 

 case, the one gamete corresponds to the sperm and the other 

 to the egg that is found in higher plants. The union is the 

 process of fertilization. The oospore may germinate imme- 

 diately, but more often it remains dormant for a period of 



