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 
of chromosomes; thase 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. 
Forthe 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 
Fie. 90.—Tetraspores. 
