1907] HOLM—RUELLIA AND DIANTHERA 327 
In the middle there is an arch of thin-walled stereome in two or three 
layers between the endodermis and the leptome. The leptome has 
very narrow sieve tubes and companion cells, and the hadrome con- 
sists of rather narrow vessels in many short rays. In the two small 
mestome bundles the mestome is less developed, and there is no 
stereome. Raphidines abound in the leptome of all three veins, 
sometimes filling the cells completely. 
There are thus in the leaf of Dianthera several features indicating 
the immediate relationship of the genus, illustrated by the structure 
of the stomata and the presence of raphidines and cystoliths. The 
distribution of stomata and palisades on both faces of the leaf at 
least points toward the general structure of an aquatic plant. 
THE PETIOLE 
There is a short but very distinct petiole, which is approximately 
hemi-cylindric in outline, the convex face being the dorsal. The 
internal structure is almost identical with that of the midrib. There 
are the same tissues of the same development, but distributed in a 
somewhat different way; for instance, the collenchyma surrounds 
the colorless parenchyma almost completely, being interrupted only 
by one narrow group of palisades in the middle of the ventral face, 
and by two small groups of the same tissue on the sides of the carinate 
dorsal, and very near its edges. There are three mestome strands in 
the center, the outline and minor structure of which agree in all 
respects with the midrib. The petiole has no stereome; cystoliths 
were found in the epidermis and raphidines in the leptome. 
Summary 
With the exception of the polystelic axis in Dianthera, the struc- 
ture of the two plants agrees well with that of Acanthaceae in general 
as recorded by SOLEREDER, namely, the type of stomata, the glandular 
and simple hairs, the cystoliths, the raphidines, the various crystals 
of calcium oxalate, etc. These characters are some of the most 
important for distinguishing the family. 
Although Ruellia and Dianthera possess the principal character- 
istics of the family, the very different environment in which they live 
has been the immediate cause of several modifications in structure. 
