US 
natural Tamili) of Plants called Composita. 
and besides these, one or two minute processes are generally ob¬ 
servable. Stigmata revolute*. 
In the 12tli edition of Systerna Naturae, Linneus added to his 
genus Calea a fourth species, namely Calea scoparia; for what rea¬ 
son it would be difficult to discover, as it does not resemble, either 
* In the remarkable character of its re-curved florets, as well as in some other respects, 
this species of Salmea agrees with Spilanthus arloreus of George Forster (in Commentat. 
Gotting. ix. p. 66.), of which he originally formed his genus Laxmanriia ; from a very er¬ 
roneous view of its structure, however, having described the Nectarium or glandula epigvna 
as a “ germen superum the real, though imperfect, germen with its two aristae as a 
“ perianthium bidentatum,” and consequently referring the genus to Polvgamia segregata. 
When he afterwards corrected these errors and reduced Laxmanriia to Spilanthus, he 
did not discover that he had only the imperfect hermaphrodite or male plant before him. 
That Spilanthus arloreus is really dioecious, I have ascertained from the examination of 
numerous specimens collected by Sir Joseph Banks in the Island of St. Helena, where it 
forms a small tree called by the inhabitants White-wood. It is Bidens arlorea and per¬ 
haps also Spilanthus tetrandrus of Dr. Roxburgh’s List of Plants appended to General Beat- 
son’s Tracts on St. Helena ; the former being probably the female, the latter as tarved 
variety of the male plant. 
In re-establishing Spilanthus arloreus as a genus, sufficiently distinct from Bidens, Spi¬ 
lanthus, and Salmea, it will not, I conclude, be considered expedient to recur to Forster’s 
name Laxmanriia, which as far as relates to this plant is connected only with a series of 
blunders, was abandoned by the author himself, and has since been applied to another ge¬ 
nus already generally adopted. It may be distinguished by the following character, and 
named 
Petrobium. 
Involucrum polyphyllum subduplici serie: exteriore breviore, foliolis paucioribus. Re- 
ceptaculum paleaceum, planiusculum. Flosculi dioici, tubulosi, 4-fidi: Masculi: Anthe¬ 
ris exsertis; Stigmatibus acutis hispidulis : Feminei: Staminibus sterilibus; Stigmatibus 
acutis recurvis. Achenium v. parallelo compressum v. angulatum; angulis (2-3) aristatis : 
aristis persistentibus, antrorsum denticulatis. 
Arbor (Insulae S'® Helenae). ToY\a opposita, indivisa. Panicula terminals, Irachiata. In¬ 
volucrum ollongum. Paleae receptaculi squamis involucri sulsimiles. Corollulae ochroleu- 
coe, tulo arcuato-recurvo (ut capitulum primo intuitu radiatum videalur). Mas. Antheris 
nigricantilus, Iasi emarginatis, appendice upicis Irevissimo, aculo ; loculis vestigio sepli 
Iongitudinalis instructis. Fem. Staminibus sterililus dislinctis, antheris sagitlatis cassis. 
ill 
VOL. XII. 
