Phylum Rhodophyta 



[45 



In more advanced examples, the first step of development after fertilization con- 

 sists of the establishment of protoplasmic contact between the zygote and other cells. 

 These may be adjacent cells, reached directly, or distant cells, reached by the out- 

 growth of connecting filaments from the zygotes. In the generality of the group, the 

 cells with which contact is made give rise to cystocarps producing carpospores; in 

 this situation, the cells in question are called auxiliary cells. In some examples, the 

 connecting filaments, after making contact with cells called nurse cells, themselves 

 give rise to the cystocarps. The carpospores, in all of these more advanced examples, 

 give rise to diploid individuals. The diploid individuals are of the same vegetative 







'ymW''^- :^^>^^ 







^■^y 



i^ 



•«!» 





Fig. 6 — Nuclear phenomena in Polysiphonia violacea after Yamanouchi (1906). 

 a, b, c. Stages of mitosis, d, e. Stages of homeotypic division. 



structure as the haploid individuals, but do not produce spermatia, carpogonia, or 

 cystocarps. Certain cells, commonly scattered and imbedded in the body, produce 

 sets of four spores which are accordingly called tetraspores; these give rise to haploid 

 individuals. 



This account means that these algae occur typically in somata of four types: male 

 and female haploid individuals; cystocarps, being a preliminary, parasitic, multipli- 

 cative phase of the diploid stage (Janet named this stage the carposporophyte; Drew, 

 1954); and free-living diploid individuals, reproducing by tetraspores. The produc- 

 tion of carpospores and tetraspores by different individuals of identical vegetative 

 structure explains the oldest name applied to this class, namely Heterocarpea. 



Understanding of the life cycle of typical Heterocarpea has been reached only by 

 much labor and after a certain amount of confusion. The first significant observations 

 were by Bornet and Thuret (1867). Schmitz (1883) showed that the zygote makes 

 protoplasmic contact with other cells. He supposed that the contact of the zygote 

 with an auxiliary cell is a second sexual fusion {Copulation) following upon proper 



