274 DR. LILY BATTEN ON 
contain very few granules, and which pass through a lenticular patch in the 
adjacent end-walls of contiguous cells. In the central siphon this connecting 
filament is rather larger than in the pericentral, and is deeper in colour. At 
the point through which the protoplasm passes there is a lenticular 
thickening round the margin of the aperture, while the actual diaphragm is 
like a perforated plate (Pl. 22. fig. 1). There is also a lateral connection 
of the central with the pericentral siphons on the tangential walls. The 
form of the connection is uniform throughout, but the lateral connections 
are not necessarily at a uniform level throughout the articulation, during 
the whole life of the plant. 
Each siphon contains a mass of pink protoplasm, embedded in which are a 
number of red chromoplasts. The plastids are not so numerous in the 
central siphon, and in the pericentral ones they are usually arranged near 
the periphery of the thallus. The nucleus does not stain very readily, but 
after prolonged treatment with iodine may be observed in the younger 
parts of the thallus, where it is very large compared with the diameter 
of the cell (PI. 22. fig. 3). 
The apical cell is a rounded and flattened cone, filled with granular proto- 
plasm and containing a large nucleus. When growth proceeds, a thin dise is 
separated by a wall from the base of the cone, but the wall is perforated in 
five places, through which strands of protoplasm pass, one central and four 
pericentral strands. Ata later stage there is a longitudinal fission of the 
disc into a central mass and four pericentral portions. The four pericentral 
parts then become separated longitudinally by walls, but retaina protoplasmic 
connection longitudinally and laterally with the contiguous siphons and the 
central siphon respectively. As Massee has pointed out (42. p. 198 et seg.), 
the inerease in size of a Polysiphonia is the result of two methods of cell 
formation. The axial row of siphons by whieh the thallus increases in 
length is the result of the division or segmentation of the apical cell, w 
the increase in thickness is due to “ gemmation " from the axial cells, 
There is a slight variation of form in the thallus of P. fastigiata. In the 
young state the protoplasm of the central siphon fills the whole cell-cavity. 
Later, however, the wall becomes thickened, particularly in the upper and 
lower parts of the siphon. 
hile 
As a result the cell contents are shut down into 
a flattened mass, which is connected with the central siphons above and below 
by a narrow strand of protoplasm passing through the thickened walls (PI, 99. 
fig.4). In this case the pericentral siphons are connected with the central 
at a uniform level in each individual articulation, the protoplasmic strands 
penetrating the wall and uniting with the protoplasm of the cential siphon. 
There is a well-defined thickened rim visible at the point through which the 
protoplasmic strand passes from one cell into the next. There has been a 
considerable amount of controversy as to whether these openings are main- 
tained in the older state of the plant. Schmitz (50. p. 215) considers that 
