282 



F. B0RGESEN 



Fig. 29. Rhizophyllis pacifica no 

 spec, part of plant, c. l7 /i. 



Stratum inferius crassius parenchymaticum 

 e cellulis rotundatis majoribus et minoribus inter 

 se mixtis fonnatum est; hie iilic cellulae inajores 

 in series ordinatae occurrunt. 



Tetrasporangia in nematbecia explanata e 

 cellulis corticalibus orta, irregulariter zonatim 

 divisa. 



On a piece of a LithotJiamnion a small frag- 

 ment (scarcely more than Va square cm) of a 

 crustaceous alga was found, which I refer with 

 some hesitation to the genus Rhizophyllis. 



It forms an irregularly lobed crust about 

 250 [J- thick, the lobes overlapping each other. The surface is uneven, some- 

 what crispate (Fig. 29). It is easily detached from the substratum, to which it 

 is fastened by means of numerous rhizoids; these rhizoids grow out everywhere, 

 not only from the lower surface, but also from the margin. 



The concistency of the thallus is fleshy-cartilaginous. No incrustation of 

 lime is found. 



Fig. 29 shows a piece of the thallus with the margin; the numerous small 

 lobes more or less overlapping each other and at last fused together are 

 clearly shown. 



The thallus has a distinct dorsiventral structure (Fig. 30, 31). It seems 

 to increase in size by marginal divisions, performed by all the cells of the 

 margin (Fig. 31 d); in any case no distinct top-cell was observed in the material 

 at hand. Fig. 31 d illustrates the margin. It is seen that the cells near the 

 margin are mostly arranged in rows; sometimes these rows are nearly parallel, 

 sometimes diverging. The cells are smallest at the periphery. Generally they 

 are cut off by cross walls parallel to the periphery, but sometimes, too, by 

 oblique walls. All the cells are 



rather uniformly developed and 

 have tick walls, giving the impres- 

 sion that the growth has ceased 

 for the present. 



A transverse section of the 

 thallus (Fig. 30) shows a cortical 

 layer above and a thick paren- 

 chymatic tissue below. The latter 

 consists of roundish cells of very 

 different size, up to c. 40 ;j. or 

 more in diameter; the cells are 

 largest in the middle, smaller up- 

 wards and downwards, they have 

 thick walls and contain much 

 starch, especially in the upper 

 part of the tissue. 



In the parenchymatic tissue 

 in the central part of the thallus with a tetrasporangium sorus and a gland-cell. C. 230 /" 



Fig. ;o. Rhizophyllis pacifica now spec. Cross section 



