1907] HOLM—RUBIACEAE 161 
walled on both faces, except below the midrib, where the outer walls 
become moderately thickened; a difference in regard to the lumen 
of the cells is very distinct, that of the ventral face being considerably 
wider than that of the dorsal. The stomata are slightly raised, and 
the air chamber is wide and deep. 
A small water-storage tissue of two strata separates the epidermis 
from the parenchyma sheath of the median mestome strand on the 
dorsal face; on the ventral face this tissue is represented only by 
two or three cells underneath the epidermis and bordering on the 
parenchyma sheath. | 
The chlorenchyma, as already stated, is composed of two strata 
of palisade tissue on the ventral, and of pneumatic tissue on the 
dorsal. Of these the former is not quite typically developed, since the 
cells are rather low and broad. The pneumatic tissue is very open, 
the cells being irregular and branched, with wide intercellular spaces; 
cells with raphides are frequent in this tissue. There is neither col- 
lenchyma nor stereome in the leaves, and the parenchyma sheaths 
of the collateral mestome strands are thin-walled and the cells large. 
The midvein has a broad group of leptome and hadrome with nar- 
row vessels, and is partly surrounded by the water-storage tissue. 
The stipules.—The stipules in Oldenlandia are extended into two 
setae, which are terminated by a short, unicellular hair; while the 
margins bear a few (mostly three) much longer and pluricellular 
hairs, such as those described above from the stem. At the base of 
the petiole, but only on the ventral face, glandular hairs were observed. 
These have a very short stalk and resemble those of Houstonia (fig. 6); 
they are arranged in two small clusters, one on each side of the 
axillary bud, but without extending to the stipules. 
The characteristics of the genus are the complete absence of col- 
lenchyma and stereome from the stem and leaves; the occurrence of 
very large druids of calcium oxalate in epidermis, cortex, and pith of 
the stem; also the pluricellular, pointed, and glandular hairs. But 
neither stem nor leaves indicate in their structure that the plant is a 
hydrophyte, any more than do the species of Houstonia. 
HovusToNIA COERULEA (HEpyorTipEsE B. et H.) 
The species is herbaceous, but perennial. The primary root is 
of short duration and soon becomes replaced by a number of secondary 
