ECTOCARPALES 



133 



Generally two kinds of reproductive structures are present, the 

 plurilocular and unilocular sporangia, but some species possess a 

 third type, the meiosporangia. The unilocular sporangia always 

 occur on diploid plants and they give rise, after meiosis, to numerous 

 haploid zooids which may either function as gametes or else develop 

 without undergoing a fusion. The sporangia are sessile or stalked 

 and vary in shape from globose to ellipsoid, the mature ones 

 dehiscing through the swelling up of the centre layer in the wall. 

 The plurilocular sporangia, which are either sessile or stalked, 

 range from ovate to siliquose in shape and are to be found on 

 haploid or diploid thalli. In E. siliculosus they represent modified 



C B D ^ E A 



Fig. 89. Ectocarpus. A, E. confervoides, plant ( x 0-44). B, E. tomentosus, unilocular 

 and plurilocular sporangia ( x 100). C, meiosporangium, E. virescens. D, mega- 

 sporangium, E. virescens. E, microsporangium, E. virescens. (A, B, original; 

 C-E, after Kniep.) 



lateral branches and arise as side papillae from a vegetative cell in 

 the filament. The plurilocular sporangia are divided up into a 

 number of small cells, each one of which gives rise to a zooid and, 

 when ripe, dehiscence takes place by means of an apical pore, the 

 contents either germinating directly or else behaving as gametes. 

 The gametes are usually aHke in size but the sex function becomes 

 weaker with age so that relative sexuality is induced, the older and 

 weaker gamete behaving as the opposite sex towards the younger 

 and stronger gamete. 



In one species, E. secundus (Gifjordia secundus), there is well- 

 marked anisogamy because there are two types of plurilocular 

 sporangia with large or small loculi that produce zooids which diflfer 



