Holtz: OBSERVATIONS ON PELVETIA. pe 
of growth; and to some extent they divide both radially and 
vertically, but not tangentially. These two rows of cells also 
have rather thin walls, although there is some thickening at. the 
angles. They are also densely packed with chromatophores. 
Below the above-mentioned cells are three or four (five) con- 
centric rows of cells that pass over into the pith on the inner 
side. Their walls are considerably thickened with a gelatinous 
substance, which, however, is firmer and denser than that of 
the pith. These walls stain deeply. The cells of these rows 
contain color grains but in more loosely disposed masses. ‘The 
protoplasmic sac’is more easily seen around these masses of 
chromatophores than in the outer cells. These cells have nearly 
’the same radial diameter as the cells in the second and third 
rows, but are generally twice as wide tangentially and twice as 
long vertically as those of the third row. ‘There is more or less 
variation in the number of rows of each of these different sizes 
of cells. These elements may be diagrammatized asin P/. LYX., 
Om, 5. 
_ The original walls between these cells thicken as the pith is 
approached. The cells lose their rectangular shape more and 
more towards the pith till at last it is sometimes difficult to dis- 
tinguish them from the more cylindrical pith cells. The cells 
remain in communication through pits, the cells anastomosing 
frequently. The longer cells form transverse septa, which are 
often oblique to the lateral walls. These septa are never 
thickened, but remain very thin and, to all appearance, allow 
protoplasmic communication (Pl. LX., /7g. 72). 
Pith. —(Pl. LX., Figs. 1-5.) The pith of the stipe and lamina 
is distinguished by the fact that the cells are separated widely 
by intercellular jelly, which in the lamina is from two to three 
times as thick as the diameter of the cells imbedded in it, less 
thick in the stipe (1-2). The pith is also marked off by the 
jelly not staining as deeply as the intercellular matrix in the 
cortex. With some stains, fuchsine for example, the stain may 
be almost completely removed by washing, leaving the inner 
wall of the pith cells colored. Pith cells are slightly com- 
pressed corresponding with the flattening of the stipe or lamina 
(Pl. LX., Fig. 1). They are nearly as wide as the average 
width of the cortex cells, and are about as long or a trifle longer 
than these. They are crossed by delicate septa (P/. LX., Fzgs. 
2, 4, 13). Pith cells are joined into vertical rows or filaments 
