136 Dwellers of the Sea and Shore 



bridged over In some way if the seaweed is to per- 

 petuate itself. It accomplishes this through its most 

 remarkable sexual reproduction. On a certain part of 

 the frond it develops an organ called the antheridium. 

 This gives rise to sperms which, like the tetraspores, 

 are Vvithout cilia and are, therefore, unable to swim. 

 However, instead of sinking to the bottom, they float 

 about until they come into contact with another organ 

 on the plant known as the oogonium. The oogonium 

 is a bottle-shaped female organ with a long narrow 

 neck. In the bulbous base is contained an egg. When 

 the floating sperm reaches the oogonium it clings some- 

 where along this neck, and, perforating the wall at the 

 point of adhesion, it passes its contents to the egg, thus 

 fertilizing it. 



Strangely, the immediate result of this fusion of the 

 sex cells is not, as one would anticipate, the develop- 

 ment of a new plant. Instead, the now fertile egg 

 breaks up Into numerous spores, and there appears in 

 the place of the oogonium a fruitlike structure called 

 the cystocarp. So what we have here is really a kind 

 of sporangium or spore case containing asexual spores. 

 But, unlike the tetraspores which cannot defer their 

 development, these carpospores can await a favorable 

 time or situation before proceeding to maturity; that 

 Is to say, before growing into a new generation of sea- 

 weeds. We find, then, in summing up the life history 

 of the red alga, that beside having two modes of re- 

 production, asexual and sexual, they produce two sorts 

 of asexual spores : The tetraspores, arising from a 

 simple sporangium; and the carpospores, products of a 

 fertilized egg developed v/lthin the cystocarp. 



