1907] HOLM—RUELLIA AND DIANTHERA 321 
nodes of the rhizome and of the ascending shoots, in the slender as 
well as in the more or less swollen portions of the vegetative axis. 
In the nodes the polystelic structure becomes somewhat obscured by 
the anastomoses of the steles; nevertheless, the presence of several 
steles is usually recognizable. 
In outline the rhizome is obtusely hexagonal and smooth; no 
stomata, but small, sessile glandular hairs were observed. Forma- 
tions of cork develop from the epidermis, including the cells with 
cystoliths (fig. 16). Inside the epidermis there is a continuous zone 
of very thick-walled collenchyma of about six layers, bordering on 
the cortical parenchyma. The cortex consists of numerous strata of 
thin-walled cells, which are round in transverse sections and with 
relatively wide intercellular spaces (fig. 17); starch was observed in 
the cortex, and numerous bundles of true raphids, but no chlorophyll. 
Throughout the internodes of the rhizome (and also of the aerial 
shoots) the cortical parenchyma represents a homogeneous tissue 
from the periphery to the central portion, whether a central stele is 
present or not. No central pith is differentiated in the internodes 
except where there is a central stele, also a small tissue of this paren- 
chyma is to be found in the peripheral steles. It appears as if the 
horizontal internodes of the rhizome have always six peripheral and 
one central stele; these steles are cylindrical and each is surrounded 
by a thin-walled endodermis with the Casparyan spots plainly visible 
and with deposits of starch. Inside the endodermis are a few cells of 
thick-walled stereome, but too few to form a sheath. In the periph- 
eral steles the leptome and hadrome form an almost complete ring, 
with a small central pith; in the central stele, on the other hand, the 
mestome is arranged in two arches, with a broad parenchyma in the 
middle. 
Between the leptome and hadrome are a few strata of cambium, 
and between the strands of mestome are three or four rays of thick- 
walled parenchyma. Raphidines (fig. 18) were observed very fre- 
quently in the leptome. 
Rico), D. glabra B. et H. (Costa Rica), D. incerta Brandg. (Lower Calif.), D. ovata 
Walt. (Florida), D. parvijolia B. et H. (Texas), D. pectoralis Murr. (St. Croix), and 
D. sessilis Gray (St. Domingo). Of these nine species I had only dried material, 
which was quite sufficient for a study of the steles, but not of the anatomical structure 
in general. 
