616 MR. S. LE M. MOORE S STUDIES 



material — is to the effect that in the newly formed cell a ring of 

 dense parietal protoplasm arranges itself round the debouching 

 point of the filament connecting it with its neighbour, just as it 

 would arrange itself anywhere else upon the wall. The pit con- 

 tinuing to deepen, two closely apposed pieces of protoplasm 

 are strung upon the pit-traversing thread. Where the pit does 

 not appreciably deepen (Ballia callitricha, Callithamnion sp.), 

 the ring has a somewhat different appearance. I cannot therefore 

 acquiesce in Schmitz's statement, that a plate of highly refractive 

 substance i3 placed at either side of the pit-closing membrane, 

 for surface views almost always show the bright contour of a 

 ring ; the highly refractive substance upon the membrane some- 

 times met with (e. g. Chylocladia articulata, secondary rings of 

 Delesseria alata) is, I venture to think, brought there subse- 

 quently to the formation of the ring. 



One point worthy of mention a propos of the comparison of 

 these cells with sieve-tubes is this : — The cell-protoplasm is fre- 

 quently found to be densely aggregated on one side or on both 

 sides of a ring. Good examples of one-sided aggregation are 

 found in the long cells from old chambers of Chylocladia articulata 

 (fig. 60), of two-sided in Halurus equisetifolius (fig. 61) : in the 

 latter type cords of protoplasm may frequently be seen passing 

 from a plate-like aggregation at the top of the cell to the more 

 fluid protoplasm lying beneath it. 



Kunning down the cell from stopper to stopper is sometimes 

 found a stout band formed of dense, completely investing more 

 fluid, protoplasm. Ballia callitricha shows this better than any 

 other type studied by me (fig. 57) r such a band may sometimes 

 traverse the lumen of the axial cells of Ceramium rubrum ; and as 

 its calibre is equal to that of the pit, the impression is produced 

 of a cord coursing uninterruptedly through several of the cells 

 (fig. 62)*. I would suggest that this may be a means whereby 

 more rapid molecular transference is effected. 



With reference to the question whether the substance of which 

 the bright contour of the rings is composed be really protoplasm 

 I would merely remark that there seems no reason why it should 

 not be so regarded. Archer f showed that the stoppers of Ballia 

 are soluble in boiling caustic potash ; and this is also the case 



* A somewhat similar disposition of the protoplasm is figured by Hick {I- c - 

 tab. 243, f.6) in the axial cells of Ceramium acanthonotum. 



t L. c. p. 214. 



