206 PHYLUM VI. RHODOPHYCEAE 



singly ("monospores") or in groups of fours ("tetra- 

 spores"); these float away and on germination give rise 

 to new plants. They are generated heterogamically by 

 the union of non-motile sperms with enclosed eggs, 

 usually resulting in the growth of branching, sporebearing 

 filaments, mostly covered, and constituting a primitive 

 many-spored fruit ("cystocarp"). 



319. In those species (by far the greater number of the 

 Red Seaweeds) in which tetraspores are produced, these 



give rise to the sexual plants which 

 are mostly dioecious. The carpospores 

 from the latter give rise, in their turn, 

 to the tetrasporic plants. The nuclei 

 of the latter possess the diploid number 



FIG. 90. Tetraspores. < t. j.i_ r J.T. j? 



of chromosomes; those of the former 

 the haploid number, the reduction of chromosomes tak- 

 ing place during the divisions leading to the production 

 of the tetraspores. 



320. Here the dominant characters are the reddish 

 pigment added to the chlorophyll of the cells, and the 

 development of the zygote into a sporiferous, usually 

 covered, tissue (the spore fruit; cystocarp). The im- 

 portant secondary characters are the definite and final 

 attainment of heterogamy, and the mostly symmetrically 

 branched and basally rooted plant body. 



For the most part the Red Algae grow at very consider- 

 able depths in the waters of the ocean, although a few 

 occur near the shore, and a very few live in fresh water. 

 They are more abundant in the warmer waters, and be- 

 come less frequent as we go toward the poles. The 

 number of known species is about three thousand. 



321. This phylum as a whole is poorly understood. 

 Very little consideration has been given to the physical 

 modification these plants have suffered through living 



