118 BOTANY. 
creeks and rivers we have an example of a filamentous plant 
of the class Zodésporee. It is a large, dark-green, much- 
branched plant, which attaches itself to stones and timbers 
in the water. It grows so vigorously that it soon forms long 
matted masses, often several metres in length, which float 
and wave back and forth in the currents of water. It pro- 
duces myriads of zodspores. 
246. The Sea-Lettuce (Ulva), which is common along the 
coast and in brackish waters, grow- 
ing upon stones, wharf-timbers, etc., 
and resembling small lettuce-leaves, 
, reproduces by zodspores. The 
~~) plant is composed of a couple of 
J layers of cells, and in some of these, 
by internal cell-formation, zodspores 
are produced; these escape into the 
water, where they swim about by 
means of their two cilia. 
Fie, 51.—A plant of Sea-let- ‘ : 
tuce (Ulva lactuca). Retural «247. Kelp and its Allies (Phzo- 
= spore) make up a large group of 
zoospore-bearing plants. They are all marine, often attain 
a great size, and are of an olive-brown color. They con- 
stitute the Kelp which is often so abundant on the sea- 
shore after a storm. 
248. The large, flat, leaf-like kelp (Laminaria, commonly 
called Devil’s Apron) may be taken to illustrate the larger 
forms. The “leaf” portion is sometimes from one to six 
metres long and nearly a metre in breadth, while its stalk 
sometimes attains a length of two to four metres. It is 
held to rocks and stones at or below low-water mark by 
means of root-like processes. 
249, The zodspores, which have two cilia, are pine 
