THE ALGH 231 
296. Gross Structure. — Examine some fresh or preserved material 
and note: 
(a) The size, shape, and texture of single plants, the mode of 
branching, and the slimy coating of the 
entire plant. 
(b) The location of the air-bladders. 
(c) The mode in which the plant is 
attached to the rock by an expanded 
holdfast. 
(ad) The enlarged fruiting tips, or re- 
ceptacles, of some branches. Draw. The 
growing point is in a pit at the tip of 
each branch. 
297. Reproduction. — Study the recep- 
tacles of different plants, cutting some 
of them across, and note that there are 
two kinds, differing in shape and in the 
external color and color of the contents. 
With a two-inch objective or a magnifying 
glass sketch a cross-section of each kind of 
receptacle showing the distribution of the 
conceptacles (Fig. 164), each opening by a 
pore to discharge its contents. 
Pick out with the point of a scalpel the 
contents of a conceptacle of each kind and 
examine with m.p. Note: 
(a) The sterile hairs. 
(6) The sac-shaped antheridia borne on 
branching hairs (Fig. 162). 
(c) The nearly spherical odgonia, large 
cells from each of which eight eggs are 
developed.t 
Observe that while the conceptacle 
shown in Fig. 164 contains both antheridia 
and oégonia, those of Fucus vesiculosus contain only one kind of 
sex organ. 
Fie. 161. Part of Thallus 
of a Rockweed (Fucus 
platycarpus). (Natural 
size.) 
The two uppermost branch- 
lets are fertile. 
1 Prepared slides with stained sections of conceptacles may be studied ta 
advantage. 
