126 A TEXT-BOOK OF BOTANY 
stricted to any special depth, they are characteristic of the 
deeper waters in which Alge grow. The red Algz are very 
little used by man, probably the most conspicuous article 
of commerce obtained from them being Irish moss, used in 
jelly-like preparations, which is the dried bodies of certain 
forms abundant in the North Sea. 
75. Reproduction.—The reproduction of the red Alge 
is very peculiar, being entirely unlike that of the other 
Alge. No swimming spores 
are produced, but sporan- 
gia occur that produce and 
discharge spores without 
cilia and hence without the 
ability to swim. Since each 
sporangium usually  pro- 
duces four such _ spores, 
they are called tetraspores 
(Fig. 118). Floating about 
in the water instead of 
actively swimming, they 
Fic. 118.—The sporangium (.!) and dis- finally germinate and_ pro- 
charged tetraspores (B) of one of the 
red Algw.—After Tourer. duce new plants, as do the 
swimming spores. 
The sexual reproduction, however, is most remarkable, 
but is too complex to be presented in any detail in an 
elementary text. The sperms, like the tetraspores, are 
without cilia and simply float into contact with the odgo- 
nium, whose form is like that of a flask with a long narrow 
neck (Fig. 119, A). In the bulbous base of the o6gonium 
the egg is developed. In a very simple case the floating 
sperm comes in contact with the long neck, the two walls 
become perforated at the point of contact, the contents of 
the sperm enters and passes to the egg, and thus fertili- 
zation is accomplished. As a result of fertilization there 
appears on the plant a spore-containing structure like a 
