ON SOUTH-AMERICAN APOCYNACEX. 143 
The above specimen, with the aspect of a Dipladenia, is only 7 in. long, with a 
straight, erect stem, with the fragment of another conjoined at the base. The basal 
opposite leaves are diminished to the size of small ovate bracts; in the superior axils 
they are only 3 lines long ; the superior three pairs, 1 in. apart, are erect, 14-14 in. long, 6-9 
lines broad above the middle, on petioles scarcely 1 line long. The terminal panicle has 
an erect peduncle bare at its base for 21 in., and bears, above, 4 flowers à in. apart, 
on bracteolate pedicels 7 lines long; sepals 5 lines long; basal contraction of tube of 
corolla 5 lines long, its entire length being 21 lines; segments 7 lines long, 5 lines 
broad; the colour of the flower is apparently purplish red; the stamens are inserted 
6 lines above the base of the tube, on a densely pilose ring ; the anthers acuminate, 
rigid, with 2 basal obtuse parallel prongs; the compressed filaments are fixed in front 
above the sinus of the forks, as in R. crassifolius, with which its floral characters corre- 
spond in all respects. 
PRESTONIA. 
This genus was established by Robert Brown in 1811, upon one of the rare plants 
collected by Banks and Solander at Rio de Janeiro in 1768. This, however, was only 
imperfectly described by that celebrated botanist, as he failed to observe the peculiar 
structure of the fruit, which was also unknown to Kunth, De Candolle, Endlicher, 
Müller, and the authors of the ‘Genera Plantarum.’ The latter botanists (op. cit. ii. p. 709) 
amalgamated with it the genus Hemadictyon, because in both cases the tube of the 
corolla is furnished in the mouth with a callous ring and 5 free narrow linear 
appendages. Under the head of Hemadictyon the reasons will be given more fully 
for refusing to adopt this conclusion. One good discriminating character has been 
overlooked, viz. the presence of several small stipules upon the transverse ridge at 
each node, and the involucel of several stipuliform scales where the peduncle of the in- 
florescence rises laterally out of the ring, which are always wanting in Hemadic- 
tyon. In the latter genus the peduncle of the raceme is always simple; in Prestonia it 
is very shortly branched, each branch densely furnished with almost sessile flowers, 
forming a capitate head, and the fruit is an elongated coriaceous 2-celled capsule. The 
inflorescence and floral structure are well illustrated in Delessert’s *Icones” (v. tab. 51), 
with one oversight, the 2-celled ovary being shown as 2 distinct ovaries. The following 
is offered as a more correct diagnosis of the genus. 
Prestoni, R. Br. : Hemadictyon (in parte) auct. Sepala 5, acute oblonga, imbricata, sequalia, aut minora 
et coriacea vel majora et submembranacea, singula intus squamulis singulis latis apice denticulatis 
munita, Corolla hypocrateriformis; tubus late cylindricus, calyce paullo longior, fauce subcon- 
strictus et illic annulo calloso integro vel callis plurimis minutis in seriem simplicem disposi- 
tis signatus, et sub faucem appendicibus 5 squamaceis cum segmentis alternis præditus; M 
menta 5, acute inzequilatera aut dolabriformia, tubo subbreviora, dextrorsum —9 cl 5, 
e pilis medio tubi orta; filamenta brevissima; anthere lineares, m = subcohærentes, apice 
acuminatæ, imo incurvatim biaristatæ, apicibus interdum subexsertis. Discus cylindricus, margine 
