CYTOLOGY OF PLANTS 271 



number of comparatively lowly organisms, the majority 

 of which dwell submerged beneath the surface of fresh 

 or salt water. In such members of the green algae as 

 have so far been examined from this point of view, it 

 would appear that the 2 ^-generation is exclusively 

 represented by the single cell which arises as the 

 actual product of conjugation between a pair of 

 gametes. Reduction takes place in the actual zygotic 

 cell, so that each of the products of this cell's division 

 shows once more the reduced number of chromosomes. 

 Thus the great bulk the vegetative mass of the 

 species is constituted by the ^-generation, and the 

 2%-generation is composed of a single cell only a state 

 of things which is exactly the reverse of what is to be 

 seen in the higher animals. 



In the vegetable kingdom evolution seems to have 

 been accompanied by a gradual increase of the 2%- 

 gene ration, and a corresponding reduction of the 

 ^-generation in point of importance. Between the 

 two extremes afforded by the algae on the one hand, 

 and the flowering plants on the other, we can trace a 

 series of intermediate stages represented by types in 

 which many other features also must be regarded as 

 standing on intermediate planes of organization. 



As an example of an intermediate condition of this 

 kind, we may take the case of the ferns. 



The fern plant, as commonly understood, represents 

 the 2#-generation. The method by which the life- 

 history of the fern plant is continued is by the forma- 

 tion of unicellular reproductive bodies which are 

 known as spores. The formation of the spores takes 



