176 SEAWEEDS 



one nucleus, and the disc-shaped chromatophores 

 one pyrenoid. 



The Reproductive Organs. Gametes with two cilia 

 are produced by the ordinary vegetative cells in 

 Ulva, Enteromorpha, Monostroma, and Pringslieimia, 

 and their conjugation in pairs has been observed. 

 There is no apparent difference to be seen among 

 them. The zygotes so formed germinate by the pro- 

 duction of a short cell-row in Ulva, and the formation 

 of a globular body in Monostroma bullosum by cell- 

 divisions in all directions. This globular body after 

 enlargement forms a hollow bag, and eventually 

 bursts, when the thallus resembles the other species 

 of Monostroma. The zoospores are of similar origin 

 to the gametes, are larger, and have each four cilia. 

 In Monostroma Wittrockii the zoospores (?) have only 

 two cilia ; but it is possible that they may be in reality 

 gametes which germinate without conjugation. 

 However, Pringsheimia, of which the gametes are 

 known, has definite zoospores with two cilia. 



The Geographical Distribution is world-wide, and 

 extends to fresh-waters in the case of Monostroma 

 and Enteromwplia. Ulva enters brackish waters in 

 all parts of the world, but Letter stcdtia, which is 

 purely marine, has a very restricted range, occurring 

 only on the coast of Natal (and Australia ?). Ilea is 

 an inhabitant of brackish waters in Europe and 

 North America, and is often known by the name of 

 CapsosipJion. All the genera except Letterstedtia 

 occur in British seas. Species of Enteromorpha 

 form the " grass " which causes to a very large 

 extent the fouling of the bottoms of ships. 



