204 ALG&. [CHAP. 



forks ; the blade being pressed in while the stem is 

 fresh and soft, is securely fixed by contraction of the 

 latter in drying 1 . But probably the most remarkable 

 genus of these dark-spored Alga is Macrocystis. 



" From a much-branched root springs, in the first 

 instance, a small forked frond which alone bears the 

 fruit in clouded patches. . . . Besides this, however, 

 arise one or more tall, slender stems, several feet in 

 length, with a vertical, terminal, lanceolate frond, 

 which is repeatedly split from the base upwards in 

 such a way as to form new leaves, the attenuated 

 base of which gradually passes into a short petiole, 

 which becomes inflated above into a bladder. The 

 original frond is thus repeatedly divided in a secund 

 manner, till the plant becomes hundreds of feet long. 

 As, however, the stem does not increase in strength 

 as the plant elongates, the strain is at length so 

 great, notwithstanding the numerous bladders, that 

 it at last gives way, and the plant floats. Many 

 species have been proposed by authors, but all are 

 reducible to one, M. pyrifera, which girds the southern 

 temperate zone, and stretches up from thence along 

 the Pacific to the Arctic regions, through 120 degrees 

 of latitude. This plant, like the Sargassum, has 

 been celebrated by all voyagers, to whom it is of 

 great value in indicating the presence of rocks, acting, 

 as it does, like a great buoy. Vast masses are thrown 

 up on exposed coasts, where it is rolled by the waves 

 till it forms cables as thick as a man's body. Single 

 plants have been estimated on reasonable grounds as 

 attaining a length of 700 feet." Berkeley. 



Mr. Darwin, in his " Voyage of the Beagle," gives 



