/ 



Carpo- 

 spore 



i^" 



-m 



i 



180 A TEXTBOOK OF THEORETICAL BOTANY 



and the diploid nuclei from the fertilized carpogonia. Since many trichogynes 

 may be involved and many simultaneous fusions have occurred there may be 

 as many as a hundred diploid nuclei from different carpogonia. 



The monoploid nuclei disintegrate, while the diploid nuclei migrate to 



the periphery of the central cell, where 



each divides into two. A lobe appears 



on the central cell at each of these 



/ points, and one daughter nucleus 



/ " enters it and the tip of the lobe is cut 



off as a cell. The other nucleus re- 

 mains in the central cell. This process 

 may be repeated so that chains of cells 

 are cut off in basipetal succession, the 

 number of chains being ultimately de- 

 pendent on the number of carpogonia 

 which were fertilized. These cells en- 

 large and become spherical, and are 

 finally constricted oflF as separate 

 carpospores. They separate and 

 escape through the ostiole of the 

 female conceptacle. 



The carpospores germinate within 

 twenty-four hours and give rise to new 

 plants identical in structure with the 

 parents, but the nuclei contain the 

 diploid instead of the monoploid 

 chromosome number. These are the plants which will ultimately produce 

 tetraspores and are therefore sporophytic plants. 



I 



'^ 



*^^^*,/>^ .j 



^^ 



Fig. 172. — Corallina officinalis. Longitudi 

 nal section of a mature female concept 

 acle with carpospores. 



Asexual Reproduction 



The disc cells of the developing asexual conceptacles divide into two, 

 the lower half forming a stalk cell, while the upper becomes the tetraspore 

 mother cell. This latter cell grows and assumes a clavate form. Its nucleus 

 enlarges and undergoes two divisions during which meiosis occurs. This 

 reduction division takes place at about the time when the conceptacle has 

 been completely developed. Wall formation follows meiosis. These walls 

 are laid down one above the other so that a row of four tetraspores is 

 produced. Such a method of septation is said to be zonate (Fig. 173). 



The tetraspores are liberated through the ostiole of the conceptacle and float 

 about freely in the water (Fig. 174). They become attached to a suitable sub- 

 stratum, such as a rock face, and germinate, giving rise to sexual plants again. 



The life-cycle of Corallina therefore shows an alternation of generations 

 between gametophytes, carposporophytes and tetrasporophytes as in Poly- 

 siphonia, Chondriis and Ceramium, though there is only a relatively simple 

 carposporophyte, compared with other members of the Cryptonemiales. 



