402 NATURAL HISTORY OF PLANTS. 
an Oceanian species very nearly connected with Acronychia, is distin- 
guished from it by its simple leaves, pentamerous flowers, and 
uniovulate ovary cells. 
Skimmia, consisting of Asiatic shrubs, with alternate simple 
leaves, have polygamous-dicecious flowers with four or five im- 
bricated petals, an isostemonous androceum, a 2-5-celled ovary, one 
ovule in each cell, and a drupaceous fruit, the stones each containing 
an albuminous seed, with one or several embryoes.  Casimiroa 
consisting of Mexican trees with an analogous floral formation, have 
for fruit a large pomiform drupe, with monospermous stones but 
exalbuminous seeds and the alternate leaves are compound-digitate. 
Phellodendron, of which only one species is known, a native of 
Manchouria, also has isostemonous flowers, but 5-8-merous poly- 
dicecious pisiform glandular drupes, with five monospermous stones 
and opposite imparipinnate leaves. : 
Ptelea trifoliata. 

Vie. 445. Fra, 446. 
Flower (3). Long. sect. of female flower. 
Pitavia nearly approaches the Zanthoxylons proper, and the Quas- 
sias (Simarubee). In Pitavia, all the species being natives of America, 
the flowers are unisexual, tetramerous, with imbricated corolla, eight 
stamens, and independent ovaries, each supporting a gland above 
and without. The fruits are drupaceous and indehiscent, and 
the leaves opposite or ternate. In the Pentaceras of Australia 
analogous to Pifavia by their independent ovaries, surmounted by 
a gland, the pentamerous diplostemonous flowers are also consti- 
tuted like those of numerous Simarubee : but the fruits are samaras, 
and the alternate leaves imparipinnate. 
Ptelea (figs. 445, 446), often connected with Zerebinthacee, con- 
stitutes alone a subseries very remarkable by the organization 
of the fruit. The flowers are polygamo-diæcious, 4—5-merous, 
isostemonous, with a single ovary, and two or three biovulate 
cells. The fruit is a widely-winged veined samara, with two or 
