158 



A TEXTBOOK OF THEORETICAL BOTANY 



of starch and are deep red in colour. They are finally liberated and pre- 

 sumably germinate to produce the tetrasporic plants, though the stages in 

 this process have not been followed in detail. 



Fig. 



The Tetrasporangium 



145. — Chondrus crispus. Nemathecium 

 containing carpospores. 



The asexual reproductive organs appear on the tetrasporic plants between 

 December and March. The nemathecia may be recognized by holding the 

 frond to the light when they may be seen as elongated dark spots near the 

 tips of the younger fronds. 



The internal tissue of the nemathecium contains irregular rows of cells 

 which form protoplasmic connections with the collecting cells and assimilating 

 cells. The cells in these rows gradually enlarge, become filled with starch 

 and are dark red in colour. Each functions as a tetrasporangium. At first 

 it is possible to see the regular arrangement of these cells in rows, but as they 

 enlarge still further they become displaced, while the surrounding sterile 

 cells give up their food material and collapse, forming the cavity of the 

 nemathecium, which is filled by the developing tetrasporangia (Fig. 146). 



The nucleus of the tetrasporangium now divides into four, during which 

 meiosis occurs, resulting in the formation of four monoploid nuclei. A 

 wall is then laid down across the cell, and in each cell thus separated a further 

 wall is formed, which may be laid down in the same plane or at right angles 

 to the first one. In this way four tetraspores are produced in a cruciate 

 group. The arrangement in which the tetraspores are produced in the 

 Rhodophyceae is an important point in classification. The tetraspores 

 germinate to produce fresh sexual plants. 



Chondrus follows the same general life-cycle as in Polysiphonia (see 

 p. 168), in which there is also an alternation of sexual and asexual generations, 

 but with one important difference. As a result of sexual fusion quite an 



