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 

 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 



