78 PLANT-LIFE 



weeds, there is much, diversity of structure and size. 

 There are small species whose thalli consist of simple 

 threads of cells at the one extreme, and, at the other we 

 find forms with complex thalli, sometimes many yards in 

 length, differentiated into a strong rootlike holdfast, 

 sturdy stem, and a flattened frond. All the forms are 

 multicellular, and it appears that in the more complex 

 species certain cells are told off for particular functions. 

 Thus, some cells act as carbon assimilators, others as 

 conductors of the products of assimilation, and still 

 others serve to strengthen the thallus. Most of the 

 Phseophycese are propagated by zoospores; but in the 

 ranks of the Wrack family (Fucaceae) we find that egg- 

 cells and spermatozoids are formed, and propagation is 

 entirely sexual. 



It is within the family Laminariacese that we have 

 the giants of the marine forest. Two species are com- 

 mon in the Laminarian zone of the British coasts, 

 Laminaria digitata and L. saccharina. The former 

 attaches itself to rocks t>y means of a strong, fibrous 

 holdfast; it has a stout stem as thick as one's thumb, 

 and its leaf is deeply lobed or cut into narrow segments. 

 It grows to a length of above 6 feet. L. saccharina has a 

 relatively short stem, and a long, flat, ribbon-like leaf 

 which may reach a length of 12 feet, with a width of 

 about 16 inches. This species is popularly called the 

 l< Devil's Apron." Chorda filum, variously termed 

 " Sea Laces," " Lucky Minny's Lines," " Dead .Men's 

 Eopes," is of the same family. Its long, slender, cord- 

 like frond must be familiar to every coast visitor; he 

 sees specimens on the shore, between tide-marks, and 

 out at sea in several fathoms of water, where it annoys 



