TYPES OF CRYPTOGAMS; THALLOPHYTES 221 
or cilia. Dissect, by picking and by friction under a cover-glass, a 
bunch of antheridia and note the branching filaments upon which 
they are borne. 
Make drawings to illustrate the various points of structure. 
282. Number of Antherozoids required for Fertilization. — The bulk 
ofan odsphere has been 
estimated to be equal 
to that of thirty thou- 
sand to sixty thousand 
antherozoids, but ap- 
parently an odsphere 
may be fertilized by 
only one antherozoid. 
Yet a large number 
swarm around each 
oésphere after both 
have escaped from the 
conceptacles, andoften 
their movements are 
so active as to cause 
the rotation of the 
odsphere. The proc- 
ess of fertilization may 
be discerned in fresh 
material by squeezing 
oéspheres and anther- 
ozoids. from their re- 
spective conceptacles 
into a drop of water 
on a slide. In some 
species, as Fucus platy- 
carpus (Fig. 154), an- 
theridia and odgonia 
Fic. 157. Transverse Section of Conceptacle 
of a Rockweed (Fucus platycarpus). 
(x about 35.) 
are found in the same h, hairs; a, antheridia; 0, odgonia. 
conceptacle. 
283. Alge.— Pleurococcus, Spirogyra, and Fucus, which 
we have just studied, are but a few types of several families 
