ee _ s 
1907] HOIM—RUELLIA AND DIANTHERA 317 
nent midrib, above and below the mestome bundles. This tissue is 
also represented, though less developed, on the leptome side of the 
secondary veins, but only the stronger ones that proceed from the 
base of the midrib. 
In proportion to the size of the leaf-blade, the chlorenchyma is 
- very thin and consists of one layer of typical palisades on the ventral 
face, and of an open pneumatic tissue on the dorsal; the latter is 
composed of two to three strata of oblong or more or less roundish 
cells with very wide intercellular spaces. The chlorenchyma is 
partly interrupted by the collenchyma above the midrib, but the 
palisades extend for some distance through the water-storage tissue 
above the mestome bundles of the midrib (fig. 6). According to 
VESQUE (I. ¢., p. 333), the palisade tissue is continuous, that is, not 
interrupted by collenchyma, in Ruellia maculata and R. formosa, in 
various species of Eranthemum, Strobilanthes, Beloperone, etc., but 
interrupted, as described above, in Sanchezia, Ebermayera, etc. 
All the mestome bundles are collateral; those that constitute the 
midrib are arranged in a broad arch with the concave face turning 
upward; the others follow the chlorenchyma in one plane. Only 
the smallest ones, which are not accompanied by water-storage 
tissue, have a closed colorless and thin-walled parenchyma sheath. 
The midrib is composed of several (mostly five) mestome strands, 
separated from each other by strata pertaining to the water-storage 
tissue; the hadrome consists of a few rows of rather narrow vessels, 
with three to four in each row. The leptome (fig. 5) is well-repre- 
sented as several groups underneath the hadrome, and also occurs 
as small, isolated strands between the hadromatic rays (L in jig. 5). 
No closed parenchyma sheath is observable in the midrib, but there 
is nevertheless an endodermis. This very characteristic sheath is 
represented here on the leptome side only; it is thin-walled, like the 
adjoining water-storage tissue, and shows very plainly the spots 
named after Caspary. Without forming a closed sheath, the endo- 
dermis thus forms an arch parallel with the keel, and ceases outside 
the leptome of the two outermost mestome strands. A like structure 
in regard to the open endodermis in the midrib is described by 
Router (J. c.) as characteristic of certain species of Thunbergia, for 
instance, T. fragrans, T. hastata, and T. hirta. 
