SPHACELARIALES (ISOGENERATAE) 159 



being arranged in whorls with tufts of hairs just below their apices. 

 Cells just below the apex divide to give a number of branch 

 segments, this type of branching being known as polyhlastic. The 

 main axis is corticate and primarily polysiphonous, because the 

 subterminal cells divide to form cortical cells which then divide 

 again several times, but as there is also an outer cortex of rhizoids 

 a pseudo-parenchymatous structure is ultimately formed. Both 

 unilocular and plurilocular sporangia are formed on stichidia which 



Fig. 109. Cladostephus verticillatus. A, plant (x ^). B, apex to show origin of 

 branch. 6a = branch apex. C, thallus showing cortication. D, unilocular 

 sporangia ( x 225). E, part of thallus with unilocular sporangia ( x 45). (A, D, E 

 after Newton; B, C, after Oltmanns.) 



arise from the rhizoidal cortex in the internodes between the 

 whorls of vegetative branches. The two different types of sporangia 

 occur on separate plants, the unilocular on what must be the diploid 

 generation as they produce zoospores, and the plurilocular on what 

 must be the haploid generation because they produce isogametes. 



Stypocaulaceae : Stypocaulon (stypo, coarse part of flax; caulon, 

 stem). Fig. no. 



The pinnate frond arises from a well-marked basal system, the 

 plants in summer having the appearance of shaggy tufts whilst in 



