PRINCIPAL GROUPS OF PLANTS. 29 



cavities, called conceptacles, and these contain the reproductive 

 organs. These consist of oogonia and antheridia, which may be 



FIG. 14. Some common marine algae. A. Laminaria, showing portions of three leaf- 

 like thalli and hold-fast; B, dichotomously branching thallus of Fucus; C, Sargassum, or 

 "gulf weed," showing a thallus resembling a leafy branch, with swollen, berry-like air 

 bladders, which act as floats; D, Dasya, a delicate branching filamentous sea-weed, attached 

 to a blade of eel-grass; E, dichotomously branching thallus of Chondrus, or Irish moss; 

 F, leaf-like thallus of Grinnellia; G, densely, but delicately branched thallus of Polysiphonia. 

 A, B, C are Brown Algae and D, E, F, G are Red Algas. 



present on the same or on different plants. The egg cells and the 

 sperm cells escape into the sea-water, and after their union an 



