213 



upon both sides of the frond ; their development is quite in 

 accordance with those of Dictyota dichotoma as described by 

 Thuret^). They are developed from a group of the epidermal 

 cells. The cells in the periphery of such a group are sterile; 

 these cells are lengthened, mostly the innermost, and bent some- 

 what towards the middle forming a kind of 

 involucre round the proper antheridial cells 

 in the middle. When the antherial cells 

 have reached a certain length a small basal 

 cell is cut off at their base and the large 



upper cell is divided verv regularly into a great ^. , „„ ^ . 



" Fig. 163. Dictyota ere- 



number of quite small cells. Seen from above nuiata J. Ag. Part of 



the antheridia are more or less polygonal by a group of antheridia 



1 ,„. ^„^^ 1 ^o ^ g^gj^ irom above. 



mutual pressure (Fig. 163). (About 90 : 1). 



The oogonia occur hkewise upon both 

 sides of the frond and their development is quite in accordance 

 with the description and figures of Thuret et Bornet^). Groups 

 of epidermal cells become lengthened and when they have reached 

 a certain length a small cell is cut off at their base, while the 

 upper large cells grow into the oogonia. Individuals with tetra- 

 sporangia were not found. 



Found once only, growing upon buoys in the harbour of Christian- 

 sted, St. Croix. 



Geogr. Distrib. Pacific Ocean at the shores of Mexico, West Indies. 



8. Dictyota dentata Lamx. 



Lamouroux, Exposit. des Caract. du genre Dictyota (Journ. de Bo- 

 tanique, t. II, 1809, p. 42). Kutzing, Species Algarum, p. 556; Tab. Phy- 

 cologicse, vol. IX, pi. 35, fig. I. J. Agardh, Species Alg., vol. I, p. 96. 

 J. Agardh, Till Algernes Systeinatik, 2dra afdeln., p. 98. J. Agardh, Ana- 

 lecta algologica, Contin. I, 71. F. Hauck, Meeresalgen von Puerto-Rico. 

 (Englers bot. Jahrb., Bd. 9, 1888,'p. 466). A. Vickers, Phycologia Barba- 

 densis, pi. XIV. 



All the specimens collected being sterile I cannot give any 

 information as to the organs of reproduction ; but Hauck (1. c.) 

 gives a short description of the tetrasporangia-bearing plants as 

 well as of the oogonia and antheridia which occur in separate 

 plants. 



Thuret, G., Recherches sur la fecondation des Fucacees et les anth6- 

 ridies des algues, 2. partie, (Ann. des Sciences Nat., 4. serie, t. Ill, 

 1855, p. 5, pi. 2). 

 Thuret, G. et E. Bornet, Etudes phycologiques, 1878, p. 53, pi. 27 — 30. 



