IT Y D 
■fig. 2, on the annexed Engraving. A leaf of it is alfo 
represented on the Botany Plate IV. fig. 34. 
|3. H. natans, or Italian floating hydrocotyle, has very 
Bender fimple fibres collected into a head, ifluing from 
the joints of the Items, and fattening themfelves into the 
mud. Stems horizontal, thick, even, flefhy, tinged with 
brownifli red, horizontal, jointed, floating. A Angle leaf 
comes out from each joint, on petioles a fpan long or 
more, curved inwards, thick at the bafe, flefhy, growing 
thinner at the top; the leaves are kidney-form, cxenate- 
lobed or repand, with five large lobes, the middle one 
fmall, the two or three others with three-lobed notches; 
in front they are cut to the very centre with a fcarcely 
gaping finus, as in H. American?.. All of them are 
floating. Flowers from five to ten, fmall, collected into 
a head. Seeds comprefled, femiorbiculate. The pedun¬ 
cles are three inches long, and iflue from the joints of the 
fem. The leaves are not peltate and emarginate, as in 
the common fort, but kiddey-form and fublobate, the 
Items thick, and the petioles very flefhy. It feems to ap¬ 
proach nearer to H. Americana. Native of Italy. 
2. Hydrocotyle umbellata, or navel wort: leaves pel¬ 
tate, crenate-gafhed, umbels many flowered. According 
to Linnaeus it is very like the common fort, and has been 
confounded with it; but it differs in having the fcape 
twice as long as the leaves, and more than twenty florets 
in a fimple umbel. Native of Jamaica, in marfhes; of 
feveral parts of the continent of America ; and alfo of 
Cochin-china; if the plant which thefe authors defcribe 
be the fame. 
3. Hydrocotyle Americana, or American navel wort: 
leaves kidney-form, fublobate, crenate. This has the 
appearance and fize of the firft. The leaves are cut in 
front to the very centre with a finus that fcarcely gapes, 
and are divided at the edge into nine obfolete lobes, each 
of which has three fmaller notches. Native both of 
North and South America, and the Eaft Indies. 
4. Hydrocotyle hirfuta, or hairy navelwort: liirfute, 
•leaves kidney-form, lobate, crenate; whorls four-flowered'. 
Native of Hifpaniola. 
5. Hydrocotyle Afiatica, or Afiatic navelwort: leaves 
kidney-form, toothletted. This difFers from the fourth 
fpecies in having the toothlets or notches round the leaves 
equal, the fubftance alfo of the leaves is twice as thick, 
and they are almoft hoary, and there are feveral together 
at each joint of the (talk, -whereas in that they are iingle. 
Native of the Eaft Indies, Japan, the Cape of Good 
Hope, Jamaica, &c.. Introduced here in 1774 by Mr. 
Francis Mafl’on. 
6. Hydrocotyle Chinenfis, or Chinefe navelwort: leaves 
linear, umbels many-flowered. This is of the fame fize 
with the foregoing forts. Native of China. 
7. Hydrocotyle villofii, or * vi?.ofe navelwort: leaves 
cordate, entire, villofe. Root fibrous; leaves petioled, 
undivided, quite entire, refembling tliofe of the fweet 
violet (Viola odorata), mucronate, tomentofe, both at 
the roots, and about the extremities of the Items, which 
are proftrate, and have flowers at the ends with the leaves. 
Flowers fmall. Native of the Cape of Good Hope. 
8. Hydrocotyle glabra, or fmooth navelwort: leaves 
obovate, fmooth. This alfo is a native of the Cape of 
Good Hope. 
9. Hydrocotyle virgata, or ftriped navelwort: leaves 
linear, fmooth. P'ound at the Cape of Good Hope by 
Thunberg. 
10. Hydrocotyle linifolia, or linear navelwort: leaves 
H YD 
<527 
gamia, and named it Solandra, from the amiable and 
learned Dr. Solander, who found it at the Cape of Good 
Hope; in the Supplement, however, and in the fourteenth 
edition of the Syftema, it is removed into this genus, 
with which it certainly agrees in habit. 
12. Hydrocotyle tridentata, or trifid navelwort: leaves 
wedgc-fhaped, trifid, villofe. This is very like the pre¬ 
ceding, but differs in having linear leaves, narroXver to¬ 
wards the bafe, with three equal teeth at the end ; not 
ovate, and five or feven toothed, as in that; peduncles 
much (hotter than the leaf, not equal in length; ftem 
fliorter, woolly, herbaceous, not woody and proftrate. 
The central is certainly hermaphrodite in this; Found 
at the Cape of Good Hope by Sparrmann. 
13. Hydrocotyle ranunculoides, or quinquefid navel¬ 
wort: leaves five-parted, gafhed. Found in Mexico by 
Mutis. 
14. Hydrocotyle erefta, or upright navelwort: leaves 
cordate crenate, (capes few-flowered, the length of the 
petioles. Native of Jamaica. 
15. Hydrocotyle mofchata, or feptemfid ’ navelwort: 
leaves kidney-form, feven-lobed, ferrate, villofe ; umbels 
many-flowered. Native of New Zealand. 
IIY'DROGEN, J. [hydrogenium , Lat. from water, 
and yivoy.a.i, -to become, or ytimctui, to produce.] One of 
the conftituent parts of water, and perhaps of muriatic 
acid. Though its gas is unfit for refpiration, it is not 
poifonous. Its effects on the animal economy are not 
peculiarly ftriking, but it appears to affedt the irritability 
of the mufcular fibre in a confiderable degree; and ani¬ 
mals killed by it are fuppofed to putrefy quickly. The 
latter opinion feems, however, from ChaptaPs Experi¬ 
ments, to be founded on a miftaken obfervation. See 
the article Chemistry, vol. iv. p. 156, 158. 
HYDROG'R APHER, f [from Gr. water, and 
ygaKpv, to write,] One who defcribes or draws maps of 
the fea. 
HYDROGRAPH'IC, or Hydrographical, adj. Be¬ 
longing to hydrography; belonging to a defcription or 
linear-lanceolate, hirfute, entire. This is like the pre¬ 
ceding, but the leaves are much longer; the peduncles 
more (lender, and alfo longer. Found at the Cape of 
Good Hope by Thunberg. 
11. Hydrocotyle tomentofa, or prickly navelwort: leaves 
obovate, toothed, tomentofe. The central flower being 
fertile (having fix ftamens and a piftil), and being fur- 
rounded by barren flowers, Linnaeus made a diftinct genus 
of it, placed it in the order monoecia of the clafs poly¬ 
map of the feas. 
HYDROG'RAPHY, f. The art of meafuring and de- 
fcribing the fea, rivers, canals, lakes, &c. With regard 
to the fea, it gives an account of its tides, counter-tides, 
foundings, bays, gulfs, creeks, See. as alfo of the rocks, 
(helves, lands, (hallows, promontories, .harbours ; the dis¬ 
tance and bearing- of. one port from another ; with every 
thing that is remarkable, whether out at fea or on the 
coalt. 
HYDRO'LEA, f. in botany, a genus of the clafs pen- 
tandria, order digynia, natural order of convolvuli, Jujf. 
The generic characters are—Calyx: perianthium five- 
parted; parts oblong, acute, unequal, permanent. Co¬ 
rolla : or.e-petalled, wheel bell-fiiaped ; tube (hotter than 
the calyx ; limb five-parted, fpreading; fegments ovate, 
incumbent. Stamina: filaments five, awl-lhaped, cordate 
at the bafe ; anthers oblong, curved, incumbent. Pif- 
tillum: germ ovate; (tyles two, filiform, fpreading: ftig- 
mas truncate. Pericarpium: capfule ovate, two-celled, 
two-valvCd; partition contrary, Seeds very many, mi¬ 
nute, imbricated; with an ovate large receptacle. In 
fome flowers the calyx and corolla are fix-cleft, with fix 
ftamens.— Ejfcntial Charader. Calyx five-leaved; corolla 
wheel-(haped; filaments cordate at the bafe; capfule two- 
celled, two-valved. 
Species. 1. Hydrolea fpinofa, or prickly hydrolea: ftems 
with axillary (pines, flowers cluftered, terminating. Stems 
upright, a foot high, with alternate branches. Leaves 
lanceolate, feflile, fomewhat waved, vifcid. Spines axil¬ 
lary, fpreading. Flowers, terminating, fub-feflile, few, 
cluftered. Seeds ovate, attenuated towards the umbilicus, 
very oblcurely grooved, pale brownifli red. When the 
flowers are fix-cleft and have fix ftamens,. there are three 
ftyles, and the capfule is three-celled and three-valved, 
with a three-fided partition. Native of South America. 
2. Hydrolea inermis, or unarmed hydrolea: ftem un¬ 
armed. 
