LEAVES. 



[ 381 ] 



LECIDINE^. 



ing a spiral fibre. In the more complete 

 forms we distinguish an epidermis, above 



Fig. 395. 



Vertical section of a leaf of a Melon. 



E. S, superior epidermis ; P. S, subjacent close paren- 

 chyma ; M, infra- stem atal air-space ; L, intercellular 

 space ; jP, i', fibro-vascular bundle (rib or vein) ; P. i, 

 inferior lax parenchyma ; E, i, inferior epidermis ; P, 

 hairs ; ST, stomate. 



Magnified 100 diameters. 



and below, often differing in character in the 

 two faces (see Epidermis and Stomates), 

 together with the diackyma or intervening 

 cellular mass, which varies in its characters 

 in different plants, and is traversed by the 

 fibro-vascular ribs or veins. The epidermis 

 exhibits Glands, Hairs, &c., in different 

 conditions and forms, which cannot be enu- 

 merated again here, many of the most in- 

 teresting forms being mentioned under the 

 above heads. For observing the structure 

 of leaves, when consisting of more than a 

 simple cellular plate, horizontal and vertical 

 sections are requned. The latter are easily 

 made with a sharp razor in thick and firm 

 leaves, but with delicate kinds it is necessary 

 to split a soft cork, to place the leaf care- 

 fully between the pieces and then to slice both 

 together, placing the fragments in water and 

 picking out the pieces of the leaf with a 

 needle. Many small simple leaves make 

 good objects by drjang, soaking in turpen- 

 tine and mounting in balsam: the same may 

 be done with petals, sepals, &c. The leaves 

 of water-plants, such as of VaUisneria, Ana- 

 charis, Ceratophyllum, Hoftonia, &c., are 

 very favourable for the observation of the 

 rotation of the cell-sap (see Rotation). 

 They are of very simple cellular structure, 

 having no epidermis, stomates or fibro-vas- 

 cular ribs. 



LECANACTIS, Eschweiler. — A genus of 

 Graphideae (Gymnocarpous Lichens), con- 

 taining one British species, L. lynceaz=.Ope- 

 grapha lyncea of the British Flora. 



BiBL. Hooker's Brit. Flora, ii. pt. 1. 

 p. 148; Leighton, Ann. Nat. Hist. 2 ser. 

 xiii. p. 391. pi. 7. fig. 25. 



LECANORA, Ach.— A genus of Leci- 

 dineae (Gymnocarpous Lichens), consisting 

 of numerous species growing chiefly on rocks, 

 stones and earth, distinguished from Lecidea 

 by the epithecia having a thickish border 

 formed of the crust and of the same colour. 



BiBL. Hook. Brit. Flora, ii. pt. 1. p. 190; 

 Eng. Bot. pi. 949, 1792, &c. 



LECIDEA, Ach. — A genus of Lecidinese 

 (Gymnocarpous Lichens), containing nume- 

 rous British species. The apothecia have a 

 border of the same colour as the disk. 

 Growing chiefly on rocks, sometimes on 

 bark. L. geograjjhica, growing on subalpine 

 rocks, is a remarkable species. 



BiBL. Hook. Br. Flora, ii. pt. 1. p. 177; 

 Engl. Bot. pi. 245, &c. 



LECIDINE.E.— A family of G\Tnnocar- 

 pous or open-fruited Lichens, characterized 

 by free, circular, ultimately convex shields, 

 with the disk always open, and placed in a 

 special excipulum. 



Synopsis of British Genera. 



I. Stereocaulon. Thallus cartilagi- 

 nous or somewhat woolly, branched and 

 shrubby. Apothecia top-shaped, sessile, 

 solid, flat, scarcely rising above the border ; 

 the disk at length spreading, covering the 

 border and reflexed. 



II. Cladonia. Thallus somewhat 

 shrubby, branched, rarely simple, rough with 

 scales, which are at length often evanescent; 

 branches cartilaginous, rigid, fistulose, all 

 attenuated and subulate, divided, fertile, 

 generally perforated in the axils. Apothecia 

 sessile, circular, convex, shaped like little 

 heads, not bordered, fixed by the circum- 

 ference, free beneath in the centre, the sides 

 reflexed, uniform within. 



III. BcEOMYCES. Thallus crustaceous, 

 spreading, adnate. Apothecia circular, con- 

 vex, head-like, not bordered, sessile upon a 

 solid stalk. 



IV. Lecidea. Thallus crustaceous, 

 spreading, adnate, uniform. Apothecia cir- 

 cular, sessile, plano-convex, having a border 

 of the same colour as the disk. 



V. Umbilicaria. Thallus foliaceous, 

 coriaceous-membranous, pustuled, fixed by 

 the centre, peltate. Apothecia circular. 



