CONJUGATION 49 



which becomes adult. Some of them, smaller ones, 

 behave with a surprising difference. Instead of 

 germinating, these latter swim a while and then unite in 

 pairs, completely fusing the two small offspring into one, 

 which is twice as large as either. After uniting, this 

 resulting cell germinates and produces a new plant very- 

 much as the swimming spores do. Here we find two 

 methods in one plant, somewhat similar and yet with a 

 most important difference. (See the figure on page 28.) 



This difference is so important and plays such a part in 

 the reproduction of all higher forms that we must examine 

 it more carefully. The new point is that offspring, instead of 

 developing, unite by twos. This union is not reproduction, 

 although it starts the development of a new plant. Instead 

 it is just the opposite of reproduction. The plant 

 reproduced when the divisions occurred that formed the 

 swimming spores. When these unite in pairs there are 

 only half as many individuals as before the unions. There 

 has been decrease instead of increase. 



The individuals resulting from the union of the two 

 cells are more vigorous and more capable of development 

 than either of the cells was before the union. The union 

 has a value in connection with reproduction; but it is not 

 reproduction. 



3. Gametes. Single-celled offspring thus may have 

 either of tvv^o fates: (1) they may develop without union 

 of any sort, in which case we call them spores; or (2) 

 they may unite by twos to form a body that develops with 

 especial vigor. In this case we call them gametes, which 

 means mates or uniting bodies. You will see that this 

 new united body is formed very differently from the way 

 in which spores are formed. The union probably means 

 something in strength and vitality for the next generation. 



In the illustration above, all the gametes are of the 

 same size and form. No one could in any way tell them 

 apart. Such union of similar cells we call conjugation. 



