MARINE ALGAE FROM EASTER ISLAND 



83 



long rows of large cells are present (Fig. 31 a); they are bent here and there 

 and their occurrence seems upon the whole to be rather accidental, parts of the 

 thallus being quite destitute of such cell-rows. They are formed by large, 

 subcylindrical to barrelshaped, thick-walled cells, about 100 ;j. long and 6; [i 

 across. In the scarce material I have not been able to follow them to the 

 margin or to explain how they are formed. In the description of Rhizophyllis 

 in ENGLER & PRANTL, Naturl. Pflanzenfam., I. Teil, VI. Abt, p. 531, the midrib 

 is described as follows: >der Hauchseite genahert verlauft in der Thallusmitte 

 eine gegliederte Centralachse, 2 zeilig alternierend in die Zahne und Lappen 

 des Thallusrandes hinein verzweigt*. If we compare this description with that 



Fig. ji. Rhizophyllis pacifica nov. spec, a— c transverse sections of thallus; d marginal portion 

 e cross section of margin, a c. 80 /i, b, c 60 /i, d 186 /i, e 2T0 A- 



given above, there is a considerable difference, as I have not observed any 

 branches from the tube of the long cells, nor is it arranged in such a way 

 that it can be called a » Centralachse*. 



The parenchymatic tissue gradually passes into the cortical layer above. 

 The latter is composed of small rounded cells arranged close together in short 

 rows of 2—3 cells which become smaller toward the surface. Seen from above 

 they form a very dense epidermal layer composed of quite small cells, only 

 4 — 5 a in diameter and with very thick walls. The epidermal cells of the 

 lower surface are larger, polygonal and c. 40—50 [t across. 



Scattered in the cortical layer we finally come across the large characteristic 

 gland-cells (Fig. 30). They are oval-pyriform, often even somewhat lageniform, 

 c. 35 u. wide and 75 ;j. long, with their broadly rounded base sunk deep down 

 into the parenchymatic tissue, penetrating with their attenuated summit between 

 the cortical cells to just below the upper surface of thallus, leaving a small 



