SECT. ii. ARBORESCENT ALG^E. 251 



or oblong lanceolate frond. This frond divides at the 

 base ; the fissures extend upwards so as to form two 

 petioles, each of which swells into an oblong or pyriform 

 air-vessel. Another fissure is formed in a similar way 

 a little above, and so on, till a single frond may at the 

 same time have eight or ten fissures, each of which 

 will ultimately gain the common apex. The margins 

 of the fissures are at first perfectly smooth, but they 

 soon become ciliated like the outer edge. The con- 

 tinuity with the fibrous base is at last broken, and the 

 divisions of the leaves going on indefinitely, the whole 

 reaches the length of some hundred feet, forming enor- 

 mous floating masses which are wafted by the waves 

 hundreds of miles from their origin. Fructification 

 only takes place in young plants ; consequently in such 

 as are still attached to their native rocks. Even in that 

 youthful state, Mr. Darwin mentions that such is the 

 buoyancy of this powerful weed, that there is scarcely 

 a loose block of stone on the coasts of Cape Horn that 

 is not buoyed up by it. 1 The Macrocystis is native 

 on the shores of the Atlantic, from Cape Horn to 43 S. 

 latitude; but on the Pacific coast, according to Dr. 

 Hooker, it extends to the river San Francisco in Cali- 

 fornia, and perhaps to Kamschatka. The plant isr epro- 

 duced by pyriform cells, full of endochrome, in nearly 

 parallel rows imbedded in the fronds. 



The rocky coasts of the Falkland Islands are covered 

 with a vast growth of the gigantic Macrocystis mixed 

 with forests of the arborescent Lessonia, which forms 

 large dichotomous trees with a stem from eight to ten 

 feet high and a foot in diameter. The leaves are two 

 or three feet long, drooping from the forked branches 

 like weeping willows. In the Lessonia nigrescens the 

 quadripartite endochrome, ultimately resolved into 



1 ' Voyage of the Adventurer and Beagle,' by Mr. Darwin. 



