RED SEAWEEDS 207 



(1) at such depths (where the Hght is greatly modified), 

 and also (2) in waters of such considerable salinity. It 

 is probable that this modification has masked their true 

 relationship to other plants, as well as to one another. 



322. One of the lowest of the Red Algae is the common 

 "Laver" (Porphyra), of the class Bangioideae, of all 

 coasts, in which the erect, deep purple, leaf-like, and 

 basally rooted, plant body is composed of a single layer 

 of cells. They propagate by monospores borne in the 

 cell layer. In their very simple generation certain cells 

 of the cell layer divide into non-ciliated sperms, while 

 others become very slightly modified into oogones, each 

 containing a single egg. The latter is fertilized by the 

 entrance of the sperm through an opening in the cell 

 wall, after which the zygote develops into usually eight 

 spores. The fruit is thus of very simple structure. 



323. In Nemalion (which with the succeeding plants 

 belongs to the class Floeideae), a branching, filamentous 

 marine Red Alga, the clustered antherids 

 produce small spherical, non-ciliated 

 sperms. The oogone is prolonged into a 

 slender structure, the trichogyne, and to 

 this latter the sperm adheres and fertilizes 

 the egg. After fertihzation the egg divides, 

 and each new cell sends out short crowded 

 branches which bear terminal spores. Here no protec- 

 tive envelope covers the spores, the fruit being very 

 simple. Asexual reproduction is not known. 



324. Here may be noted briefly the Corallines (Coral- 

 lina) which are filamentous Red Algae which become so 

 heavily coated with lime as to effectually hide their cells. 

 This lime coating is like an ancient coat of mail with its 

 flexible joints at intervals. The antherids and oogones 

 are in separate terminal cup-shaped structures, those con- 



