78 EVOLUTION OF PLANTS 



Protococcacese, while others may have sprung from 

 forms allied to the Confervacese. 



The second subsidiary order of green algse, the 

 Conjugatse, 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. 



In the Characese we encounter a very circumscribed 

 and specialized group of plants. of doubtful affinities, 

 showing no certain relationships with any other groups 

 of algse, and possibly best removed from the Algse alto- 

 gether and made the type of a special sub-kingdom. 



Among the brown algse 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 

 Chlorophycese, but even in the highest types both egg- 

 cells and spermatozoids are discharged into the water 

 like the zoospores of the lower forms. 



The red algae show a marked divergence from the 

 Chlorophycese, 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- 



