208 PHYLUM VI. RHODOPHYCEAE 
taining the oogones becoming the fruit after fertilization. 
Tetraspores occur in similar cup-shaped structures. 
325. Polysiphonia contains plants in which the branch- 
ing, filamentous plant body is composed of more than one 
row of cells, usually of a central row surrounded by an 
outer layer, completely covering it. These shallow- 
water plants are often of marked beauty both in struc- 
ture and coloring. The tetraspores are 
produced in unmodified or slightly swollen 
branches, and originate within the tissues, 
but with the increase in size of the tetra- 
sporangia they eventually reach the surface 
and slip out as large, deeply colored naked 
Polysiphonia. cells. The special antheridial branches 
consist of a central axis with numerous 
short, crowded, radiating branchlets whose extremi- 
ties (antherids) abstrict the naked, colorless sperms. 
The oogone possesses a trichogyne, and is surrounded by 
a few protective cells. The sperms carried by currents 
of water come in contact with the trichogyne, and 
attach themselves to it and form cell walls. The nucleus 
of one passes into the trichogyne, and unites with that of 
the oogone. The oogone now fuses (for nutritive pur- 
poses, as there are no nuclear fusions) with a large nearby 
cell (the auxiliary cell) into which the zygote nucleus 
passes, and from which arise the filaments which produce 
the carpospores. In the meantime the surrounding 
cells produce an urn-shaped structure (pericarp) with 
an opening at the top from which the naked carpospores 
escape at maturity. 
326. Irish Moss (Chondrus) is so easily obtained at the 
apothecaries that it may well be cited as one with a 
parenchymatous, much branched plant body. The 
oogones and afterward the spore fruits are immersed in 
