594 BRITTON: VEGETATION OF THE ° 
holding tissue. The cell-walls are very delicate and broken down 
in some cases though intact in others. Holm in writing about the 
structure of Carex Fraseri* considers these strands as lacunes. 
Though the .cell-walls may eventually break down completely, 
thus forming true lacunes, in the material which the writer has ex- 
amined it seems that these strands must be considered as water- 
tissue. The water-strands are surrounded by assimilating cells. 
Stomata occur on the lower surface. /P/. 26, 6, shows a transverse 
section of the leaf. 
POLYGONELLA ARTICULATA. — Leaf nearly terete, slightly flat- 
tened. Large bundle in center surrounded by large parenchyma- 
cells, and about ten small mestome bundles in the outer portion of 
the parenchymatous tissue, which is evidently formed from the as- 
similating cells as the derivation was shown in the sections studied. 
Epidermal layer made up of large bulliform cells, certain cells 
being depressed and glandular (see /. 26, a). Stomata are abun- 
dant around margin of cross-section. Between the epidermal layer 
and the central parenchyma-cells are three to four layers of as- 
similating palisade-cells containing chromatophores. The bundles 
contain spiral vessels. Central parenchymatous tissue has small 
intercellular spaces, and certain cells next to the palisade layer are 
filled with large crystals. 
The stem is of similar structure, having an epidermal layer of 
cells for holding water, but a large number of the cells are glandu- 
lar. Just inside the epidermal layer are two layers of green assim!- 
lating cells, inside of which is a more or less distinct layer of large 
circular cells. Next are ten bundles arranged radially in a circle. 
Inside the ring of bundles are large pith-cells, No stomata could 
be found on the stem. The leaf-sheaths or ocreae have large 
water-cells on the outside. Ten or eleven strands of stereome 
occur in the constricted places. 
PLATANUS OCCIDENTALIS. — Upper epidermis of leaf is or 
posed of rather small cells that appear rectangular in cross-section. 
These cells are not colorless and, as regards contents, resemble 
the palisade-cells. Palisade and mesophyl tissue very compact. 
Stomata occur on the under surface of the leaf, and both ee 
are covered especially when the leaf is young, with long branche? 
-* Holm, ee Am, Jour Sci. 1V. 3: 121-128, pl. g. 1897- 
