SOME PECULIAR VARIETIES OF ALG^E 35 



floating state, thus dispensing with the disk-like root, as it needs 

 no holdfasts, and propagating solely by lateral and axillary 

 ramification. 



There are said to be one hundred and fifty species of Sargas- 

 sum, but 8. bacciferum alone constitutes the beds of the Sargasso 

 Sea. The plant is the most highly differentiated of any seaweed, 

 in that it more nearly approaches the true leaf and stem, and is 

 described botanically as follows : Frond furnished with distinct, 

 stalked, nerveless leaves and simple, axillary, stalked air-vessels. 

 The integument is leathery, and the color brown of varying 

 shades. The most striking peculiarity is the abundance of 

 globular cells. These berry-like air-bladders give the plant buoy- 

 ancy enough to support the weight of its innumerable guests. 

 (Plate XVI.) 



THE LAMTNARIACEjE 



In the larninarian zone, described above, grow the Laminaria- 

 cece, an order of brown seaweeds, some of whose genera grow to 

 enormous size, and in some places form dense submarine forests. 

 Darwin speaks of the good service rendered by these plants to 

 vessels navigating stormy coasts, where often they act as natural 

 breakwaters, and again as buoys designating dangerous rocks 

 near the shore on which they grow. The seaweeds belonging to 

 this order, commonly known as oarweeds, tangle, devil's-apron, 

 and sea-colander, are frequently seen twelve to twenty feet in 

 length, and others are measured by fathoms. One of the giant 

 plants is Nereocystis Liitkeana, which occurs on the northwest 

 coast. It has a stalk, sometimes three hundred feet in length, 

 which bears on its extremity a barrel- or cask-shaped air-vessel, 

 six or seven feet long, from the surface of which a tuft of fifty 

 or more forked lamina? grows to a length of thirty or forty feet. 

 The stem which anchors this immense frond is so small that the 

 Aleutian Indians use it for fishing-lines. The sea-otter makes 

 his home on its huge air-vessel, and the plant is called by the 

 Russians the " sea-otters' cabbage." 



But the longest of all known plants is the alga Macrocystis. Its 

 thin naked stem, the diameter of which seldom exceeds one quar- 



