116 
THE SEAWEEDS 
associated with deeper waters, yet able to flourish m the gloom of such 
places where other plants cannot obtain sufficient light. 
The Red Algae form a well-marked but comparatively isolated group 
which arose in the Archaeozoic era. Sexual reproduction shows an alterna- 
tion of generations in which three kinds of mature individuals may be 
produced in a regular succession or life-cycle. The life-cycles of the 
Euflorideae are fairly uniform and follow one or other of the two types 
which can he illustrated by a discussion of such typical genera as Nemalion 
and Polysiphonia. In either case there occurs a fusion of non-motile 
gametes (sexual cells) with consequential nuclear fusion to form a diploid 
zygote in which formation the chromosome number is doubled to the normal 
number of the adult plant. The Reds have been compared to the higher 
seed plants (Phanerogams) in that in both cases the sperm cells are non- 
motile and without cilia and are hence passively carried to the receptive 
portions of the female organ which remains imbedded in the mother-plant. 
Fertilization affects not only the zygote formed by the fusion of the two 
sex cells, but also cells in the neighbourhood, cf. endosperm in Angiosperms 
and the so-called auxiliary cells of the Reds, both of these tissues playing 
a most important role in the nourishment of the developing sporophyte. 
In the Red Algae this takes the form of the so-called gonimoblast filaments 
from which carpospores are formed which germinate to give the mature 
sporophyte generation. Nemalion has a life-cycle typical of many of the 
simpler Euflorideae, while Polysiphonia is typical of the more advanced 
types with quite a complex life-cycle. 
(a) Nemalion possesses a tha.llus consisting of a long, dichotomously- 
branched cylinder, made up of a dense mass of interwoven, branching fila- 
ments imbedded in a gelatinous matrix. In the central portions of the thallus 
the filaments predominantly run lengthwise, with numerous lateral branches 
arising from these at right angles to form the denser outer portions. The 
cells of these filaments are uninucleate, and in addition in the outer 
assimilatory cells there is a single star-shaped plastid in which lies a 
pyrenoid surrounded by starch granules. Within the filaments adjacent 
cells are in intercommunication through continuous strands of cytoplasm 
passing through pores of various sizes on the cross-walls. 
The male sex organ is the spermatangium, incorrectly termed by some 
authors an antheridium, borne terminally in dense clusters on a short lateral 
branch easily distinguished from vegetative branches due to the fact that 
it is completely colourless, or the cliromatophore is only very poorly 
developed. The initial of such a branch arises as an apparently normal 
vegetative cell terminating a lateral filament from the central core, but then 
proceeds to cut .off a chain of 4-7 cells, each of which becomes a sperma- 
tangial mother-cell which will give rise to four radially disposed 
spermatangia. Within this spermatangium the actual male sex cell is the 
spermatium, consisting of a single nucleus and rudimentary chromatophore, 
and upon its liberation by rupture of the spermatangial wall, a new sperma 
tangium develops within the wall of the old one. 
