78 EVOLUTION OF PLANTS 
Protococcacee, while others may have sprung from 
forms allied to the Confervacee. 
The second subsidiary order of green alge, the 
Conjugate, originated probably from unicellular forms 
near the bottom of the scale, and have retained a very 
primitive type of structure, as regards both the vege- 
tative and reproductive parts. 
eIn the Characee we encounter a very circumscribed 
and specialized group of plants of doubtful affinities, 
showing no certain relationships with any other groups 
of algze, and possibly best removed from the Algz alto- 
gether and made the type of a special sub-kingdom. 
_ Among the brown alge specialization has been largely 
in the direction of great increase in size, accompanied by 
a considerable degree of differentiation, both of external 
organs and of the tissues. The evolution of the repro- 
ductive cells has not, in all cases, followed the develop- 
ment of the plant body, and the larger forms, especially 
the giant kelps, are in this respect exceedingly primitive, 
producing non-sexual reproductive cells only. Within 
the class, however, there is a development of the sexual 
cells comparable to that in the principal groups of the 
Chlorophycez, but even in the highest types both egg- 
cells and spermatozoids are discharged into the water 
like the zodspores of the lower forms. 
The red alge show a marked divergence from the 
Chlorophycez, not only in their color, but especially in 
the complete absence of motile cells. In most of them 
the spores are not formed directly from the fertilized 
carpogonial cell, but from certain auxiliary cells which 
are fertilized secondarily. This is rendered possible by 
the establishment of direct protoplasmic connections be- 
