1907] HOLM—RUELLIA AND DIANTHERA TBS 
THE STEM ABOVE GROUND 
The basal internodes are obtusely quadrangular and hairy with 
glandular or pointed hairs of the same structure as those of the 
leaves (figs. 3, 4). The cuticle is smooth, and the cells of epidermis 
are small, somewhat thickened on the outer wall, and contain cysto- 
_liths. Five layers of thick-walled collenchyma surround the cortex, 
which is thin-walled and consists of about nine strata with wide 
rhombic intercellular spaces; cystoliths and raphids occur in the 
cortex, but no sclerotic cells and no deposits of starch. A thin-walled 
endodermis surrounds the stele, which is obtusely quadrangular in 
cross-section. A few scattered stereomatic cells are located inside 
the endodermis and outside the leptome. The mestome strands are 
collateral; the hadrome is represented by short rays of vessels, 
separated by mostly four rows of thick-walled parenchyma; a few 
layers of cambium are observable between the leptome and hadrome, 
but none outside the medullary rays. The central portion of the stele 
is occupied by a thin-walled pith of large cells, several of which 
contain raphids and crystals of various forms, prismatic, rhombic, 
etc., but no cystoliths and no starch. 
The structure of the apical internodes differs in a few points 
from that of the basal portion of the stem. For instance, the collen- 
chyma occurs as separate strands interrupted by the cortex, which is 
rich in chlorophyll but contains no cystoliths. Moreover, the stere- 
ome is better developed in the superior internodes, forming an almost 
closed sheath inside the endodermis, but outside the collateral mes- 
tome bundles. 
In the nodes there is a much stronger development of the collen- 
chyma than in the internodes, and the cortex does not break through 
this tissue so as to reach the epidermis. By comparing the structure 
of a node with that of the internode below, the following deviations 
were noticed: there are ten continuous layers of collenchyma in the 
node, but only five and not continuous in the internode; there are. 
seven layers of cortex in the node, but only five in the internode. 
The stereome inside the endodermis is reduced to a very few cells in 
the node, while it is much better represented in the internode. The 
pith occupies a larger portion of the section in the node than in the 
internodes. Finally, the cells of the cortex and pith show a wider 
