SEAWEEDS AND PONDWEEDS 51 
may be considered as the father and mother respectively 
of the young plants. 
To this belong all the brown Seaweeds. The green 
Seaweeds, such as the Sea-lettuce, belong to the second 
class, the “conjugates.” A good example of the brown 
seaweeds is the well-known Bladder-wracks, which one 
may find anywhere on the beach, conspicuous by its 
inflated cells filled with air, which 
serve to keep it afloat, and its flat, 
much-branching structure. ao 
In certain parts of the plant there | a \ fo 
are pits, mother-pits and father-pits. \\o 
In the one little balls or eggs of |‘ 
protoplasm are developed, and, at 
the proper stage, they are allowed 
to pass out of the pit. Meanwhile 
in the father-pit pieces of proto- 
plasm of different shape have been 
produced, and these also pass out 
into the water and coalesce with the 
egos. The first effect of the com- 
bination is that the ball of proto- 
plasm, which was formerly naked, 
is able to build itself a cell-wall, 
and after a rest of some time, it 
becomes a full-grown Bladder-wrack 
with pits of itsown. This is certainly 
a more elaborate method than mere splitting, or even the 
coalescence of two similar cells, and marks a considerable 
step forward. ; 
In a very common fresh-water alga, called Vaucheria, 
we find a somewhat similar arrangement. Lach plant 
consists of a single branching tubular cell as a rule, but | 
BLADDER-WRACK., 
