ECTOCARPALES 



149 



may represent a transition stage from the corticated to the paren- 

 chymatous type, although it is usually considered that these two 

 forms of thallus arose independently. The unilocular sporangia, 

 which are club-shaped, are borne on branched monosiphonous 

 filaments crowded together in large oval or elongate receptacles 

 that bear a cluster of hairs at their apex. This type of reproductive 

 structure is more or less unique among the simpler forms of the 

 Phaeophyceae. 



ScYTOSiPHONACEAE : Phyllitts (phyllos, leaf). Fig. 102. 



The unbranched fronds are expanded, membranous, leaf-like 

 structures with an internal medulla composed of large, colourless 



Fig. 102. Phyllitis Fascia. A, plant ( x f). B, transverse section of thallus with 

 plurilocular sporangia ( x 375). (A, original; B, after Setchell and Gardner.) 



cells and an outer layer of small, superficial, assimilatory cells. 

 Unilocular sporangia are not known nor are there any paraphyses. 

 The plurilocular sporangia, which are arranged at right angles to 

 the surface, arise from the superficial cells and produce zooids that 



