SOME PECULIAR VARIETIES OF ALG 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 S. 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 LAMINARIACEE 
In the laminarian zone, described above, grow the Laminaria- 
cee, 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 laminew 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- 
