i6o 



PHAEOPHYCEAE 



winter they are more regularly pinnate owing to the shedding of 

 branches. The inner cortex of the central axis is composed of a 

 number of cubical cells whilst there is also an outer cortex of 

 rhizoidal cells, the whole forming a pseudo-parenchyma. Any cell, 

 whether in the inner or outer cortex, can develop a new apical cell 

 upon injury, so that there is a great power of regeneration of apical 



Fig. no. Stypocaulon scoparium. A, summer form ( x |). B, winter form ( x |). 

 C, apex, showing branches with cortication. D, unilocular sporangia. (A, B, 

 original; C, D, after Oltmanns.) 



cells. Only unilocular sporangia are known, and these are formed 

 in groups of up to fifteen on a pad of tissue in the axil of each 

 branch on the fertile shoot, but as in Cladostephus secondary 

 sporangia may arise within the empty sheaths of the old ones. 

 Meiosis takes place in these sporangia, and the zooids on germina- 

 tion give rise to new Stypocaulon plants. One herbarium plant of 

 S. scoparium with antheridia and oogonia has been reported, but 

 these may have been abnormal unilocular sporangia. In view of the 

 great interest of this observation, however, it would be very 

 desirable to have a further study made of this alga. 



TILOPTERIDALES {ISOGENERATAE) 



Haplospora (haplo, simple; spora, seed). Fig. in. 



This and Acinetospora belong to a peculiar group of algae, the 

 life cycles of which are somewhat incompletely known, but it is 



