THE BROWN SEAWEEDS. 45 



The cells grow smaller and more compact toward the outside of the section, 

 until there are no spaces of any size between those of the outside or rind. 

 The cells contain small chloroplasts like those of the higher plants, but 

 owing to the presence of the brown pigment found in all of the class, in 

 addition to the chlorophyll, they appear golden brown instead of green. 



No non-sexual reproductive bodies are known in the rock weeds, beyond 

 small branches that occur in clusters on the margins of the main branches, 

 and probably become detached, forming new plants. In some of the lower 

 forms, however, e.g. EctocarpusandLaminaria (Fig. 28, J., <7), zoospores 

 are formed. 



The sexual organs of the rock weed, as we have already seen, are borne 

 in special cavities (conceptacles) in the enlarged ends of some of the 

 branches. In the species here figured, F. vesiculosus, the antheridia and 

 oogonia are borne on separate plants ; but in others, e.g. F. platycarpus, 

 they are both in the same conceptacle. 



The walls of the conceptacle (Fig. 26, B) are composed of closely inter- 

 woven filaments, from which grow inward numerous hairs, filling up the 

 space within, and often extending out through the opening at the top. 



The reproductive bodies arise from the base of these hairs. The 

 oogonia (Fig. 26, (7, E) arise as nearly colorless cells, that early be- 

 come divided into two cells, a short basal cell or stalk and a larger ter- 

 minal one, the oogonium proper. The latter enlarges rapidly, and its 

 contents divide into eight parts. The division is at first indicated by a 

 division of the central portion, which includes the nucleus, and is col- 

 ored brown, into two, four, and finally eight parts, after which walls are 

 formed between these. The brown color spreads until the whole oogonium 

 is of a nearly uniform olive-brown tint. 



When ripe, the upper part of the oogonium dissolves, allowing the 

 eight cells, still enclosed in a delicate membrane, to escape (Fig. 27, H). 

 Finally, the walls separating the inner cells of the oogonium become also 

 absorbed, as well as the surrounding membrane, and the eight egg cells 

 escape into the water (Fig. 27, 7) as naked balls of protoplasm, in which 

 a central nucleus may be dimly seen. 



The antheridia (Fig. 26, F, G) are small oblong cells, at first colorless, 

 but when ripe containing numerous glistening, reddish brown dots, each 

 of which is part of a spermatozoid. When ripe, the contents of the 

 antheridium are forced out into the water (Cr), leaving the empty outer 

 wall behind, but still surrounded by a thin membrane. After a few 

 minutes this membrane is dissolved, and the spermatozoids are set free. 

 These (Fig. 27, A') are oval in form, with two long cilia attached to the 



