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A TEXT-BOOK OF BOTANY 



stricted to any special depth, they are characteristic of the 

 deeper waters in which Algae grow. The red Algae 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 Algae 

 is very peculiar, being entirely unlike that of the other 



Algae. 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 



USfiial ^mm%^ i n the water instead of 



A "^^ actively swimming, they 



FIG. us. The sporangium (A) and dig- finally germinate and pro- 



tetraspores (B) of one of the 



, , , . , 



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 oogo- 

 nium, whose form is like that of a flask with a long narrow 

 neck (Fig. 119, A). In the bulbous base of the oogonium 

 the egg is developed. In a very simple ease 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 



