identity of these two plants. This fact, it seems probable, will cause some confusion, since it now
appears that Porana volubilis, the type of the genus Porana, is genericallv identical with
Brewena Ronburghii, and I presume with all the other species of that genus, but is not identical
with all or perhaps any of the associated species of Porana. This is a point which it
seems necessary to examine carefully, and which, now that it is suggested, will, I trust, engage
the attention of some Botanist having adequate materials to enable him finally to dispose of
a question that may lead to the breaking up of several genera. Among the examples given in
the supplementary plate will be found, for more easy comparison, analyses of Porana volubilis
Brewena Roxburghn, and Porana racemosa. Of the latter, 2 sections of the ovary are given
one transverse, exhibiting the normal form, 2-celled, each 1-ovuled; the other longitudinal, showing
one further advanced with a solitary erect ovule; the other having already aborted as the
mature fruit is one-seeded.
“ CoNVOLVULACEAl.
Rivea, Argyreia, and Lettsomia.
M. Choisy, in his Memoir on Indian Convolvulacese, in taking up Lonreiro’s geuus Akgy-
keia, has changed its character so essentially, that every one of Loureiro’s genuine species
must now be excluded. I say genuine, because if Choisy is correct in referring Argyreia
festiva, Wall., to A. acuta, Lour., which I doubt, then that is not a true species of his genus,
which, as defined by himself, has a 4-celled ovary, while A. f estiva has'it 2-celled.
- , “re*ro.8 character of the fruit of Argyreia is ‘bacea subrotunda exsucca 4-locularis
Choisy s_ ovarium 2-loculare 4-spermum,’ If the berries in Loureiro’s plants have four cells,
it is obvious the ovary must have had at least an equal number: hence, in assigning a 2-celled
ovary to Argyreia, Choisy has altogether suppressed the original genus, and set up a most
distinct one in its place, while at the same time he has added to the confusion by placing in his
new genus, numerous species with 4-celled ovaries and fruit. In fact, nearly the whole genus,
as it now stands m De Candolle’s Prodromus, will, I apprehend, be found not to come within
ms generic character.
“I t is a curious fact, that Roxburgh fell into a similar error in regard to his genus Lett-
somia which according > his definition, has 2-celled ovaries, while nearly all his species have
them 4-celled. When both he and Loureiro wrote, the same importance was not attached to
that point of structure that M. Choisy has shown it deserved, and their error is easily traced
to too rapid generalization. Loureiro must have examined a species with a 4-celled fruit, and
took it for granted all the others had the same structure. Roxburgh on the other hand, when
drawing up the character of his genus Lettsomia, seems to have had a species before him with
a 2-celled ovary, and assumed that all the other species with baccate fruit had likewise only
wo cells. He consequently associated under that character many species with 4-celled ovaries
and only two or three having them 2-celled. M. Choisy, in the course of his examinations’
“ 7 sPe?ies having four cells, others having two cells: of the former he has constituted
the genus Rivea, of the latter his genus Argyreia. But falling into the same error
as .Loureiro and Roxburgh, he has generalized where he should have dissected, and has thereby
een induced to bring together, under his essential generic character, ‘ovarium 2-loculare ’
numerous species having ovarium 4-loculare.
With a view to the correction of these blunders, with the least amount of inconvenience
to the science, I propose retaining all the three genera, which can be very well done by
merely slightly altering the character of Rivea, and leaving the other two as defined by their
ongmal founders. For example, Choisy gives to Rivea a capitate or lamelliform 2-lobed stigma
and 4-celled ovary : I propose substituting the word linear for capitate, and referring all
CenvoUulaeeous plants having indehiscent fruit, a 4-celled ovary and linear, cylindrical, or
lamelliform stigmas, to Rivea; those with 4-celled ovaries and capitate, 2-lobed stigmas, to
wnJ T i? ’ anj-iaSt,7’ thT°®e having 2-celled ovaries and capitate, 2-lobed stigmas, to Lettsomia.
With this modification, Rivea stands in exactly the same relationship to Argyreia, that Convol-
,dr!e.s t0 Jp0m°ea, while Lettsomia forms the transition from Argyreia to Ipomoea, having
the indehiscent fruit of the one, and the 2-celled ovaries of the other.
ILLUSTRATIONS OF INDIAN BOTANY. 203
“The characters of these three genera will then stand thus :—
“Rivea.—Fruit indehiscent. Ovary 4-celled. Stigmas 2, linear, cylindrical or lamellate.
“Argyreia.—Fruit indehiscent. Ovary 4-celled. Stigmas capitately 2-lobed.
“Lettsomia.—Fruit indehiscent. Ovary 2-celled. Cells 2-seeded. Stigma capitately 2-lobed.
“Thus limited, the genera MaŸipa, Legendrea, Marcellia, Blinlcworthia 9 Humbertia, and
Moorcroftia, will probably all be absorbed by Lettsomia, along with some of the species now
referred to Argyreia, such as A. acuta (Ch.), A. aggregata (Ch.), A. festiva (Wall.), A. sestosa
(Ch.), A. elliptica (Ch.). Our genera will then possess precision of outline very favourable
for the determination of their species: as they now stand, that is wanting, and determination
is consequently most difficult, whence we now find species of Argyreia, as here limited,
referred to Rivea, Argyreia, and even to Ipomoea.”
Having premised these suggestions for the reconstruction of these genera, I shall conclude
my remarks on this family by republishing, from the Madras Journal of Science, a “Clavis
Analytica” of the Peninsular genera and species, which I often found of infinite service, prior
to the appearance of De Candolle’s 9th volume, and which I still find a valuable adjunct to the
larger work in the determination of difficult species, and at all times more convenient for
ready reference. In the suplementary plate I have introduced analyses of as many of the genera,
as I could make it accommodate.
Choisy’s tribe Cuscutece is considered by many Botanists, and not without reason, a distinct
order. I t differs widely in habit, being parasitical and leafless, and in having, moreover, a series
of scales within the tube of the corolla which, it is presumed, may be viewed as an inner row
of stamens. On this point I feel very doubtful, as we find similar appendages in many other
plants where no such origin is suspected, and moreover because I find them wanting, in one I
published in my leones, under the name of Cuscuta arabica. The habit is dissimilar, the
embryo is very different, and the scales are wanting in Convolvulacées, all legitimate grounds
for viewing them as distinct ; but still, as they have always been united, I feel disposed for the
present to retain them here.
CLAVIS AN A L Y T IC A o f the Convolvulacées o f the Peninsula o f India, by G e o r g e
W a l k e r -A r n o t t , Esa. a .m ., f .l .s . & r .s. E d in .; communicated, with observations and
figures, b y D r . W ig h t .
TO THE EDITOR OF THE MADRAS JOURNAL OF LITERATURE AND SCIENCË.
S ir—The subjoined Clavis Analytica of the Peninsular Convolvulacées (prepared and
communicated to me by G* Walker-Arnott, Esq.) I hope will prove as useful to your botanical
readers as I have found it, in determining the species of that beautiful, but difficult,
and hitherto ill-understood, family of plants. I may here premise, that I have met with
one or two errors in the first two genera, two or three species of Rivea being referred to
Argyreia, which, however, is of little consequence, as the precision of the generic characters
will soon lead to their correction. I t is proper to add, that these are not chargeable to Mr.
Arnott, he having simply reduced, to a tabular form, the species according to M. Choisy’s determination,
adding a few new ones in my collection, not seen by that gentleman when elaborating
his Memoir. Mr. A. thus writes
“As M. Choisy’s Memoir on the Indian Convolvulacées is inaccessible (being printed in a
foreign Society’s transactions), I have got a loan of it from our friend Sir W. J. Hooker, and as
Convolvulacées appears to be a favourite Order of yours, I shall here present you with a Clavis
Analytica, adapted solely to the Peninsular species, which I have made out from his specific
characters for my own use. You of course understand, that in the Clavis I reject all characters
(good or bad) that are not essential to your making out the plant : it is possible, therefore, that
ere this you may have got some new ones, in which case they, by the Clavis, may appear to
coincide with, what they are really distinct from.”
The letters, appended to the following generic names, show the successive steps of operation
in examining a plant : that at end of first step, refers to the second, the second to the third, &c.
The species, Ipomea obscura, has been selected as a favourable example, from its going
through so many successive steps. These, when put together, form a very complete character :