156 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.3 



EXPLANATION OF PLATES 



PLATE 18 



Figs. 1-2. Rhodymenia pertusa, cross sections of a tetrasporic frond 

 to show unmodified cortex, x 120 



Figs. 3-4. R. palmata, cross sections of a tetrasporic frond to show 

 the nemathecial modification of the cortex, x 130 



Figs. 5-6. R. palmetta, cross sections of (5) a tetrasporic and (6) a 

 sterile frond, x 140 



Figs. 7-8. R. australis, cross sections of (7) a sterile and (8) a tet- 

 rasporic frond. X 135 



