668 UMBILICUS. [CLASS X. ORDER IV. 



must be the formation of the plants, which flourishes so well and 

 perfectly under the greatest extremes of moisture from a dripping rock 

 to the arid and exposed situation of old wall tops, where its supply of 

 moisture is so precarious, and oft for months without any refreshment 

 from rain : from these circumstances the student will be led to in- 

 vestigate the causes why the sedums have the power to so freely 

 absorb nutriment, and so tenaciously retain it. We know that it 

 is not only by the extremity of the roots that plants absorb fluids, 

 but that they are furnished with storaata, or mouths, in various parts 

 of the plant, and in greater or less abundance, and that by these 

 they not only absorb but expel fluid and serial substances; but these 

 stomata in the sedums must be of a very different construction, 

 or extremely scanty in number or size, corapai'ed with many other 

 plants, for they exist and flourish through the drought of summer, 

 while numberless plants in similar situations have long withered, dried 

 up, and passed away. 



GENUS XXII. UMBILICUS.— De Cand. Navelwort, or 



Pennywort. 



Nat. Ord. Crassula'ce^. De Cand. 



Gen. Char. Calyx of five pieces, united at the base. Corolla mono- 

 petalous, tubular, five-cleft. Stamens ten, inserted into the 

 corolla. Ovaries five, each with a nectariferous scale at the 

 base. Styles subulate, — Name umbilicus ; the navel. 



1. U. pendulinus, De Cand. (Fig. 762.) Pendulous Navelwort, or 

 Pennywort. Leaves peltate, depressed in the middle ; roundish crenate 

 flowers; racemose numerous, pendulous ; bracteas entire. 



Cotyledon umbilicus, Huds. — De Cand. Prod. 3, p. 400. — Lindley, 

 Synopsis, p. 64. — English Botany, t. 325. — English Flora, vol. ii. p. 

 314. — Hooker, British Flora, vol. i. p. 21L 



j3. horizonialis. (Fig. 763.) Flowers erect, at length horizontal. 



U.horizontalis. — De Cand. Prod. 3. p. 400. — Cotyledon horizontalis. 

 — Guss. Prod. Fl. Sic. 1. p. 517.— Ten. Fl. Neap. App. 5. p. 13.— 

 Flora Roman Addend, p. 65, 



Moot somewhat tuberous, with long fibres. The whole plant smooth 

 and succulent, from six to about twelve inches high. Stem erect, 

 roundish, simple, or sometimes branched, leafy below, and of a purplish 

 colour. Leaves on the lower part of the stem, on long footstalks, quite 

 smooth and fleshy, orbicular, depressed in the centre, and attached to 

 the footstalk, the margins unequally notched or lobed, or crenated, the 

 upper ones more deeply cut, becoming plane, not peltate. Inflo- 

 rescence a long terminal simple raceme, sometimes branched. Flowers 

 numerous, each elevated on a pedicle, arising from the axis of a 

 simple linear bractea, nearly as long as itself, at first erect, becoming 



