THE ALG^ 



231 



296. Gross Structure. — Examine some fresh or preserved material 

 and note : 



(n) The size, shape, and textui'e of single plants, the mode of 

 branching, and the slimy coating of the 

 entire plant. 



(6) The location of the air-bladders. 



(c) The mode in ■which the plant is 

 attached to the rock by an expanded 

 holdfast. 



(d) 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. ^NTote : 



(a) The sterile hairs. 



(J) The sac-shaped antheridia borne on 

 branching hairs (Fig. 162). 



(c) The nearly spherical oogonia, large 

 cells from each of which eight eggs are 

 developed.^ 



Observe that while the conceptacle 

 shown in Fig. 164 contains both antheridia 

 and oogonia, those of Fucus vesiculosus contain only one kind of 

 sex organ. 



1 Prepared slides with stained sections of conceptacles may be studied to 

 advantage. 



Fig. 161. Part of Thallus 

 of a Rockweed {Fucus 

 platy carpus). (Natural 

 size.) 



The two uppermost branch- 

 lets are fertUe. 



