Holtz: OBSERVATIONS ON PELVETIA. ol 
The cortical part of the holdfast passes without any marked 
change into that of the stipe. The epidermal cells however are 
not elongated as much radially as those of the other parts of the 
surface of the plant. It is covered with a cuticle, thicker than 
on the stipe or lamina. 
Cross-sections of the central part of the holdfast show (/7g. 
8) that the vertical rows of cells seen on vertical section are not 
disposed in any regular order. The intercellular substance is 
not nearly as abundant as in the stipe. Toward the margin of 
the holdfast the cells show power of dividing. Here we find, 
interspersed with cross-sections of the vertical rows, sections 
through cell rows slanting up toward the axis of the plant.. Still 
nearer the outside we come upon the meristematic zone. Here 
are principally slanting rows of cells dividing dichotomously in 
the radial direction. These divisions repeat the dichotomy, 
running directly to the surface. 
All the living cells in the holdfast have chromatophores. 
The central cells contain but few grains, the cortical are crowded 
with them. | 
Stzpe. — But little need be added here to what has been said 
under tissues in general. The young stipe has a nearly cylin- 
drical structure, with a slight notch on the end where a growing 
point is situated. No differentiation is noticeable between stipe 
and lamina. Older stipes become flattened, partly on account 
of the flattening of the cells parallel with the longer axis of the 
cross-section, but more on account of the greater growth toward 
the thin margins. A cross-section of an older stipe shows two 
principal planes of fission by the arrangement of the cells in rows 
parallel with the major axis of the section and the other obliquely 
across this axis. This is especially noticeable inthe pith. The 
cortical cells show a distinctly concentric arrangement (/7g. 7). 
The only differentiation seen in cross-section is that the pith 
and inner cortex cells near the ends of the ellipse are somewhat 
larger than those of the central part. This differentiation how- 
ever does not even suggest a midrib. Longitudinal sections of 
the stipe, cut parallel to the flat surface, show a similar appear- 
ance, except that the typical pith cells are reached sooner in 
passing from the surface along the minor axis. The appear- 
ance of the cells in both cross and longitudinal sections has been 
discussed under tissues in general. 
Lamina.—The general tissues of the stipe and lamina are so 
