6 
PACIFIC SCIENCE. Vol. XIII, January 1959 
Figs. 4, 5. Drawings of portions of two intersecondary panels (secondary vein at top and bottom of each 
figure), X 10. Note scarcity of free-terminating vein endings. 
LEAF HISTOLOGY 
The general arrangement of tissues of the 
lamina of Bo^ea is distinctive enough to merit 
comment in this account. The epidermis is 
uniseriate on both leaf surfaces with the 
stomata limited to the lower. Beneath the up- 
per epidermis there is a two-layered hypo- 
dermis (Fig. 6) of rather large, closely-packed 
cells apparently lacking chloroplasts. Onto- 
genetically, the hypodermis is derived from a 
single ground meristem layer. The latter is the 
adaxial subprotodermal layer which in many 
leaves produces the palisade layer of the 
mesophyll or its equivalent. The systematic 
significance, if any, of the hypodermis in the 
Rubiaceae is not known. It does occur in the 
only other species of Bo^ea (B. timonioides) 
available for study and in at least one species 
of Timonius, a closely related genus, but has 
not thus far been found in other genera of the 
tribe (Pray, unpublished). Solereder (1908: 
445) and Metcalfe and Chalk (1950: 761) 
record the sporadic occurrence of this feature 
in several other genera of the family. The 
palisade layer, which is nearly medially situ- 
ated in the leaf, is biseriate for the most part. 
The spongy layer is quite loosely arranged, 
with the individual cells of rather irregular 
form. 
The smaller vascular bundles which con- 
stitute the minor venation extend from the 
lower limits of the hypodermis into the 
spongy mesophyll, with the conductive tis- 
sues located within the latter. As noted above, 
the greater part of the vascular bundle is 
sclerenchymatous, with individual fibers and 
fiber strands extending beyond the limits of 
the conductive tissues. There are rarely idi- 
oblastic sclerenchymatous elements in the 
areoles (Fig. 2, center). These often appear 
to be intermediate between typical fibers and 
elongate foliar sclereids, such as certain of the 
unbranched types described in Trochodendron 
(Foster, 1945: pi. IV). 
