THE THALLOPHYTES 355 
Atlantic shores and mussel beds of our inlets. They all possess 
floats or bladder-like structures con- 
taining carbon dioxide and oxygen 
which aid in buoying up the plants 
in the salt water when submerged. 
Common forms occurring along the 
eastern coast of North America are 
Fucus, Ascophyllum and Sargassum. 
The last named is called the Gulf 
Weed because it is often found float- 
ing freely in the gulf stream. Large 
numbers of these plants often ac- 
cumulate in quieter areas of the 
ocean where they form the so called 
**Sargasso Sea.” 
Fucus Vesicutosus (THE Biap- ¥ pity 
DER WRACK).—This form, a brown ea) voy 
alga, occurs as a flat thallus, which Ky 
forks repeatedly, a type of branching 
called dichotomous. It grows near 
the surface of sea water, attached to 
rocks or to mussels along banks by 
means of a basal, disc-shaped holdfast. 
In the upper branches of the thallus 
are to be found air-bladders which are 
more or less spherical and usually in 
pairs. The tips of old branches 
become swollen and are termed 
receptacles. They are dotted ES Se ok sae oe 
with minute warts, each having an North Atlantic. A, The simple 
aperture at its summit which leads type of Laminaria, some of whose 
into: aH eneieee eeuis acthads the SPete Ere: te be thirty oF more 
3 : : feet ‘long. B, The digitate type 
receptacle. This cavity is called (jominaria digitata) which is never 
the conceptacle. Within the concep- very long, but is broad at the base. 
tacles of the male plants of thespecies (from Bergen and Davis Principles 
the antheridia, or male sexual organs, — 
are formed while in the conceptacles of female plants the odgonia or 
_ female sexual organs, are produced. The conceptacles also con- 
