612 MB. S. EE M. MOORE S STUDIES 



still in the simple condition ; a view from above of the cell- 

 closing membrane with three nodules in tbe stage represented 

 at fig. 43 will be found at fig. 44. 



Polysiphonia nigkescens*. — Each branch of the frond has a 

 h ingle longitudinal series of large axial cells, every one of which 

 is surrounded by a number of smaller siphon-cells equal in length 

 to it. The axial cell communicates with every siphon-cell by 

 means of a well-defined ring, the membrane of which is every- 

 where pierced with holes (figs. 45 and 46). The rings are usually 

 placed halfway up the axial cell ; but it often happens that they 

 are not all upon the same level. The upper and under surfaces 

 of the latter cell are largely composed of membraue resembling in 

 this respect the large cells of Delesseria alata. In fig. 47 an en- 

 deavour has been made to represent this, as seen in a longitudinal 

 section through the roof and floor of two axial cells. Upon the 

 right a small portion of the very slender primary ring is visible, 

 and several secondary rings also appear in it ; although these 

 rings are small, the protoplasm distributed to them is divided in 

 passing them (as is shown, but not satisfactorily, by the ring 

 near the median line of the section). Fig. 48 represents a bird's- 

 eye view of a membrane ; several small secondary rings can be 

 distinguished at its circumference ; while upon a large part of it 

 lies a quantity of tenacious protoplasm. 



The siphon-cells are connected with their neighbours by small 

 rings with perforated membranes (fig. 50). Upon the circum- 

 ference of the axial cells at the nodes, and alternating in position 

 with the rings connecting an axial cell and its siphon-cell, are 

 placed a number of small rings ; from each of these a delicate 

 strand of protoplasm, sometimes here and there thickened, 

 emerges to pass into the small ring of a cell much less in size 

 than the siphon-cells between and beyond the outer portion of 

 which it is situated (fig. 40). Similar cells intercommunicating 

 by small rings are situated in the neighbourhood of the cell just 

 mentioned. 



Polysiphonia fastigiata differs greatly from the foregoing. 

 In the oldest condition in which I have seen it, the axial cells 

 communicate with each other by means of a small ring with per- 

 forated membrane. The protoplasts — amoeboid in appearance 

 from the presence round their equator of a number of stout pro- 

 * I have not been able to get a sight of Kolderup-Rosenvinge's 'Bidrng til 

 Polysiphonia'? Morphologi,' quoted by Schaarschmidt (/. c). 



