CYTOLOGY OF PLANTS 305 
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 alge as 
have so far been examined from this point of view, it 
would appear that the 2x-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 x-generation, and the 
2x-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 2x- 
generation, and a corresponding reduction of the 
x-generation in point of importance. Between the 
two extremes afforded by the alge 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 2x-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 
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