71 



Order 6. Dictyosiphonaceae. Dictyosiphon. 



Order 7. Desmarestiaceae. Desmarestia aculeata is common. 



Order 8. Myriotrichiaceae. Mijriotrichia. 



Order 9. Elachistaceae. Elachista fucicolu is a common epiphj'te on 

 species of Fiicus. 



Order 10. Chordariaceae. The shoot-systems are often surrounded by 

 mucilage. Chordaria ; Leathesia difformis occurs as rounded, brown-green 

 masses of the size of a nut, generally attached to other Seaweeds. 



Order 11. Stilophoraceae. Stilophora rhizodes is common. 



Order 12. Spermatochnaceae. Spermatochnus paradoxus is common. 



Order 13. Sporochnaceae. Sporoclmus. 



Order 1-4. Ralfsiaceae. Ralfsia verrucosa is common as a red-brown incrus- 

 tation on stoues and rocks at the water's edge. 



Order 15. Lithodermataceae. Some species of the genus Lithodcrma occur 

 in fresh water. 



Order 16. Laminariaceae. The thallus is more or less leathery, 

 and has generally a root-like lower part (Fig. 69) which serves to 

 attach it, and a stalk or stem-like part, terminated by a large leaf- 

 like expansion. Meristematic cells 

 are situated at the base of the leaf, 

 and from these the new leaves are 

 derived. The older leaf thus 

 pushed away by the intercalary 

 formation of the younger ones, 

 soon withers (Fig. 69). Gametes 

 are wanting. Zoosporangia are 

 developed from the lower part of 

 a simple, few-celled sporangio- 

 phore, which is an outgrowth from 

 a surface-cell and has a large 

 club-formed apical cell. The spo- 

 rangia are aggregated into closely 

 packed sori, which cover the lower 

 part of the terminal leaf, or occur 

 on special, smaller, lateral, fertile 

 fronds (Alaria). Most of the 

 species belonging to this order live 

 in seas of moderate or cold tem- 

 perature and occur in the most 

 northern regions that have yet 

 been explored, forming their organs 

 of reproduction during the cold and darkness of the arctic night. 

 Laminaria is destitute of a midrib and has only one terminal leaf. 



FIG. 69. Lammdria digitnta (much 

 reduced in size) . 



