1907] _ HOLM—RUBIACEAE 165 
lenchyma and stereome in the organs examined; the glandular hairs; 
the striate cuticle; and the presence of stomata on both faces of the 
cauline leaves. 
HOUSTONIA PURPUREA 
The rhizome is very short and condensed, being merely repre- 
sented by short internodes, the basal portion of aerial shoots. Several 
axillary buds occur on these subterranean stem portions, and some 
of these develop during the fall into small rosettes of leaves with dis- 
tinct petioles and green, almost glabrous, elliptical blades. Second- 
ary roots occur in pairs at the nodes, between the leaves, and in addi- 
tion other roots are formed near the middle of the subterranean 
internodes. 
The roots.—The secondary roots are very slender, sparingly 
branched, and not very hairy. Their structure agrees in all essential 
points with those of the preceding species, but they differ in showing 
a slight increase in thickness, due to the development of cambial 
strata in the stele itself, but without influencing the structure of the 
peripheral strata from endodermis to epidermis. It appears as if 
the secondary formations are confined to the leptome and hadrome, 
and that they are of short duration, the roots persisting only for one 
or two seasons. The capillary lateral roots are diarch, with two 
vessels in the center and two broad groups of leptome. 
The aerial stem.—The basal internodes are quadrangular, with 
the angles produced into short and very narrow wings. The cuticle 
is wrinkled longitudinally and quite thick. Unicellular, obtuse, and 
somewhat bent hairs are frequent; they are thick-walled and show 
longitudinal (not spiral) striae of the cuticle. Viewed en face the 
cells of the epidermis are rectangular, and the stomata have one pair 
of subsidiary cells parallel with the stoma. The outer and inner 
wall of the epidermis is thickened, but not the radial. Inside the 
epidermis is a cortex with chlorophyll and raphides, but there is no 
collenchyma, not even in the wings. The strata of the cortex are 
arranged very regularly in rays toward the center, and the innermost 
layer is differentiated as a thin-walled endodermis, with the Casparyan 
spots plainly visible. Directly bordering on the endodermis is an 
almost continuous band of leptome and hadrome with very narrow 
medullary rays. The central pith is solid but thin-walled, and con- 
