CONTRIBUTIONS TO BOTANY. 
195 
styrax corymbosa I have found some of the flowers with only four 
teeth in the calyx, with four petals and eight stamens, all re- 
sembling in size, shape, and structure those of Halesia, the ovary 
being at the same time of similar form, and in like manner 4- 
locellate at its base ; indeed I can perceive no difi’erence what- 
ever in the structure of the tetramerous flowers of Pterostyrax 
and those of Halesia. There is, however, a considerable disparity 
in their respective habits; and this appears to constitute the 
principal generic distinction. Zuccarini describes the calyx as 
having five nervures between the lobes ; but he omits all mention 
of the carinate nervures, which, proceeding from the points of the 
teeth, run down decurrently along the pedicel, exactly as in 
Halesia] in the latter genus we find the same intermediate 
nervures as are ascribed to Pterostyrax. The petals are spathu- 
lately oblong, membranaceous, and free to the base, as in Halesia 
diptera ; and I find their aestivation to be quincuncially imbricate, 
not sinistrorsely convolute, as stated. The stamens are quite 
similar in form to those of the species last mentioned, the fila- 
ments being broad, flat, membranaceous, and pubescent, slightly 
cohering together at the base, and even there being separable by 
the slightest force : the anthers are a very little broader than the 
filaments, the parallel cells separated by an interval, and dorsally 
adnate to the filaments, not affixed to them by their base, as they 
are described to be. As in Halesia, the ovary is half-superior, 
and in like manner has a central placenta rising to the middle, 
leaving the upper moiety l-locvdar, its lower portion being 
divided into four or five divisions, which, branching from the_ 
placenta, are continuous with as many parietal nervui-es that run 
up into the hollow style. The fruit of Pterostyrax is much 
smaller, scarcely more than one-fourth the size of that of Halesia, 
and its nut is much thinner in substance ; but its structure is 
quite analogous, leaving little doubt that it has undergone the 
same peculiar mode of growth and development as that before 
described in the latter genus. In the only seed-vessel I have 
seen, the seeds were destroyed by age. The habit of Pterostyrax 
corymbosum is more like that of Styrax Obassia, its leaves having 
the same kind of deep sharp serratures : its inflorescence, as in 
Styrax, is racemose, the racemes being many-flowered, and axil- 
lary as well as terminal in the young branchlets. Its flowers are 
smaller than those of Halesia tetraptera, and about one-third the 
size of those of H. diptera. 
The following generic character has been framed from my 
own observations 
Pterostyrax, Sieb. et Zucc. — Flores hermaphroditi. Calyx 
pai-vus, turbinatus, ovario adnatus, margine hbero, hie 4-5- 
2 c 2 
