196 



SEXUAL REPRODUCTION OF FUCUS 



larger and loses entirely the power of motion. The reproductive 

 organs, or gametangia, are developed in specialized branches or 

 enlarged tips of the thallus. In Fuciis (Fig. 121, g), these organs 

 are contained in small pits or cavities that appear as minute 

 points, or as dots when the enlarged tip of a branch is held up 

 to the light. A magnified section taken through such a branch 

 shows the nature of the cavities (Fig. 122, B, C). In some 

 species, the male and female gametangia are found in the same 



Fig. 122. Structural features of Fucus: A, cross-section of a portion of 

 the central stem-like part of the plant, showing an epidermal, e, cortical, 

 cr, and central region, c. B, section of one of the cavities that appears to 

 the eye as a dot. See Fig. 121, B, g. This cavity contains only male game- 

 tangia. C, section of activity from another plant contains only female game- 

 tangia. — x^fter Oltmann. 



cavity, or they may occur separately and on difTerent plants. 

 The male gametes are developed in enormous numbers in numer- 

 ous little sacs, or antheridia, borne on branching filaments of cells 

 which grow out from the sides of the cavities (Fig. 123). The 



