208 
PACIFIC SCIENCE, Vol. XI, April, 1957 
Fig. 1. Longitudinal section of young petiole of 
Hesperomannia arborescens subsp. Swezeyi {Carlquist H3), 
X 170. Short biseriate glandular hairs may be seen near 
the epidermis (below), interspersed among crowded 
uniseriate nonglandular hairs, which cover most of the 
photograph. 
of the leaf bears a trichome of one of these 
types. This condition is true of all of the 
species. A preparation of the most glabrous 
species, H. Lydgatei , showed an identical sit- 
uation. During enlargement of the young 
leaf of H. arborescens subsp. Swezeyi , there is 
a tendency for the uniseriate trichomes to 
degenerate and slough off. In Figure 1, the 
uniseriate trichomes already show an accu- 
mulation of dark-staining resinous contents, 
indicating the beginning of their decline rel- 
atively soon after formation. Upon matura- 
tion of the leaf of this plant (Fig. 2), uniseriate 
hairs have disappeared altogether, except for 
occasional persistent basal cells. Simultane- 
ously, the biseriate glandular trichomes in- 
crease in size and become sunken into pockets 
as the mesophyll expands. 
Differences in leaf indument, which are 
treated here as important characters of the 
species, may be explained on the basis of 
differential elimination of trichomes during 
maturation of the leaf. In H. arbuscula subsp. 
oahuensis , for example, uniseriate hairs are re- 
tained, particularly on the young stems and 
lower surfaces of leaves (Fig. 3). In this spe- 
cies, uniseriate hairs, particularly the terminal 
cell of each, become sclerified, corresponding 
with their persistence. Biseriate glandular 
hairs are also present on the mature leaf of 
H. arbuscula subsp. oahuensis. Although less 
numerous, both types of trichomes may also 
be found on mature leaves of H. arbuscula 
subsp. arbuscula. Hesperomannia arbuscula is 
the only species in which uniseriate trichomes 
are retained on the mature leaf. 
In H. Lydgatei , H. arborescens subsp. ar- 
borescens , subsp. Bushiana , and some popula- 
tions of subsp. Swezeyi ( Judd 1244 , for ex- 
ample), both types of trichomes disappear 
early in leaf ontogeny. In leaves of these taxa, 
a heavy cuticle is formed on both adaxial and 
abaxial epidermis. 
Variations in leaf thickness occur in all the 
species, and cannot be considered as a con- 
stant taxonomic character. 
Peduncle 
Among the taxa recognized here under H. 
arbuscula and H. arborescens , little variation in 
Fig. 2. Transection of a mature leaf of Hesperomannia 
arborescens subsp. Swezeyi {Carlquist H3) , X 130. Abaxial 
epidermis at left. Note vein, accompanied by scleren- 
chyma, remnants of uniseriate hairs on the abaxial 
surface, and sunken glandular hairs. 
