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 Pringsheimia, 
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 Wittrockw 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 Enteromorpha. Ulva enters brackish waters in 
all parts of the world, but Letterstedtia, which is 
purely marine, has a very restricted range, occurring 
only on the coast of Natal (and Australia ?). lewis 
an inhabitant of brackish waters in Europe and 
North America, and is often known by the name of 
Capsosiphon. 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. 
