318 BOTANICAL GAZETTE [MAY 
The portion of the blade described above was near the middle, 
where the leaf is broadest; however, the structure is essentially the 
same throughout. At the narrow apex there is only a decrease in 
width of the collenchyma, the water-storage tissue, and the midrib, 
which consists only of three almost confluent mestome strands; 
while the chlorenchyma has not undergone any change. 
Characteristic of the leaf of our Ruellia, therefore, is the interrup- 
tion of the chlorenchyma by the collenchyma, and the presence of 
isolated leptomatic strands between the rays of hadrome. The 
structure of the stomata, the presence of glandular and long pointed 
hairs, and the cystoliths are, so far as we know, characteristic of 
Acanthaceae in general. 
THE PETIOLE 
A transverse section of the very short petiole shows an approxi- 
mately crescent-shaped outline, the ventral face being almost flat in 
contrast with the dorsal, which is obtusely carinate. The structure is 
almost identical with that of the midrib in the blade. Glandular and 
pluricellular pointed hairs occur also, and two or three strata of 
thick-walled collenchyma follow the outline inside the epidermis. 
A colorless, thin-walled water-storage tissue occupies the greater 
portion of the section, and the mestome bundles are arranged in an 
arch as in the midrib, while two very small strands of mestome are 
located in the thin margins, surrounded by chlorophyll-bearing 
parenchyma. 
Cystoliths are abundant in the epidermis, but are absent from the 
colorless parenchyma, in which only raphids and some long _pris- 
matic crystals were noticed. On one side of the broad arch-shaped 
midrib two wide sclerotic cells were observed, and a few raphidines 
in the leptome. 
Dianthera americana L. 
This species is very frequent in the vicinity of Washington, D. C., 
where it grows in creeks and in the Potomac River, generally asso- 
ciated with Saururus, Sagittaria, Pontederia cordata, etc. It has a 
very long, horizontally creeping rhizome, with opposite, scale-like 
leaves and stretched internodes of an obtusely hexagonal outline. 
Secondary roots, from four to eight or even more, are developed at 
