Pattern and Ontogeny of the Foliar Venation 
of Bobea elatior (Rubiaceae) 
Thomas R. Pray^ 
Before a full understanding and appreci- 
ation of the various patterns of foliar venation 
can be attained there must be a greater knowl- 
edge of the ontogenetic processes which re- 
sult in the diverse patterns of veins. The 
ontogenetic investigations to date suggest 
that there is a correlation between the shape 
and arrangement of the plate-meristem cells 
of the young leaf which produces the minor 
vein system and the pattern of the mature 
venation. In the case of the prevalent pattern 
in dicotyledons of polygonal areoles as ex- 
emplified by Liriodendron (Pray, 1954, 1955^), 
the plate meristem concerned is composed of 
small isodiametric cells whose planes of anti- 
clinal division (with respect to the surface) 
are random; i.e., they are not oriented in any 
particular direction. The veins which com- 
prise the mature minor venation are similarly 
disposed. In Hosta (Pray, 1955^, c), a mono- 
cotyledon, on the other hand, the intercostal 
venation (i.e., that between the primary veins), 
whose course is roughly at right angles to the 
course of the primaries, is derived from a plate 
of cells elongated at right angles to the pri- 
maries. Likewise, the study of Foster (1950, 
1952) on the distinctive foliar venation of 
Qutina shows that the lineolate minor vena- 
tion is derived from similarly oriented elon- 
gate cells in the plate meristem of the 
developing leaf. 
The present study was initiated therefore to 
examine the ontogeny of another distinctive 
pattern of foliar venation as displayed by the 
leaf of Bobea elatior. The genus Bohea with five 
species is endemic to the Hawaiian Islands. 
An extensive survey (Pray, 1953: 172-264) of 
the tribe of the Rubiaceae in which it is 
placed, the Guettardeae (composed entirely 
^ Department of Biology, University of Southern 
California, Los Angeles 7, California. 
of woody trees and shrubs), has revealed an 
astonishing variety of foliar venation patterns 
which exhibit varying degrees of expression 
of a lineolate disposition of the minor veins. 
The simpler patterns present in the Guettar- 
deae appear to represent initial phases in the 
evolution of a markedly lineolate pattern of 
minor venation. Bobea, as a representative of 
those genera which display a lineolate pattern 
to a slight degree only, is of particular interest 
in broadening our understanding of variation 
in foliar venation and the ontogenetic proc- 
cesses which lead to such variation. 
MATERIALS AND METHODS 
The writer is indebted to Dr. Sherwin Carl- 
quist for providing the material which formed 
the basis for the present study. The material 
was collected on the Palolo-Mt. Olympus 
trail on the island of Oahu, Territory of 
Hawaii. Vegetative buds and leaves in various 
stages of development were preserved in FPA. 
A voucher specimen of the same material has 
been deposited in the Herbarium of the Uni- 
versity of California, Berkeley (Carlquist H6, 
August 1953). Mature leaves and those in 
several stages of development were cleared 
with 2 V 2 per cent NaOH to facilitate the study 
of the overall venation pattern. Sections were 
made at 7 and 8 /x, with a great predominance 
of paradermal sections which have been found 
to be especially important in ontogenetic 
studies of venation patterns. All sections were 
stained with tannic acid — ferric chloride — 
safranin with a weak solution of fast green 
used to further differentiate the safranin. 
VENATION PATTERN 
The leaf blade of Bobea elatior is broadly 
lanceolate and varies from 4.5 to 11 cm. in 
length and 2 to 4.5 cm. in width. As is true 
SMITHSONIAN 
INSTITUTION JAN 2 7 1959 
