i62 PHAEOPHYCEAE 



spherical uninucleate sporangia (oogonia?) borne on a stalk cell and 

 partly immersed in the branches. The asexual plant reproduces by 

 means of quadrinucleate spores formed singly in stalked or sessile, 

 terminal or intercalary, monosporangia. Meiosis has been reported 

 as occurring in these sporangia and this would be expected if they 

 were primitive tetraspores. It would appear, according to some 

 accounts, that the plants known as Haplospora glohosa and Scapho- 

 spora speciosa are simply alternate phases of one and the same 

 species. 



In Acinetospora the plant structure is very simple, the slender, 

 tufted thallus being monosiphonous throughout and frequently 

 unbranched or else with very occasional branches. No fusion of 

 zooids from either the uni- or plurilocular sporangia has been 

 observed, and so this alga must either be regarded as the simplest 

 member of the Tilopteridales in which sexuality has not yet wholly 

 developed, or else as a degenerate member in which the sexual 

 organs have been lost or highly modified. This latter view is prob- 

 ably the more satisfactory in view of the position of the family as 

 a whole. 



Plants with unilocular sporangia only occur in April and May 

 and the swarmers give rise to plants bearing plurilocular sporangia. 

 It has recently been suggested that the monospores are a means 

 of vegetative reproduction, e.g. morphologically equivalent to 

 propagules. 



REFERENCES 



Sphacelaria. Clint, H. B. (1927). Publ. Hart, Bot. Lab. no. 3, p. i. 

 Stypocaulon. Higgins, E. M. (193 i). Ann. Bot., Lo?td., 45, 345. 

 Acinetospora. ScHMmx, P. (1940). Ber. dtsch. Gesell. 58, 23. 

 Cutleria. Yamanouchi, S. (1912). Bot. Gaz. 54, 441. 



