LECANORA. 



[ 456 ] 



LEIBLEIXIA. 



fibre. In the more complete forms we dis- 

 tinguish an epidermis, above and below, 

 often differing in character on the two faces 

 (see EPIDERMIS and STOMATA), together 

 with the diachyma or intervening cellular 

 mass, which varies in its characters in dif- 

 ferent plants, and is traversed by the fibro- 

 vascular ribs or veins. The epidermis ex- 

 hibits GLANDS, HAIRS, &c., in different con- 

 ditions and forms, which cannot be enume- 

 rated again here, many of the most inter- 

 esting 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 required. The latter are easily 

 made with a sharp razor in thick and firm 

 leaves ; but with delicate kinds it is neces- 

 sary to split a soft cork, to place the leaf 

 carefully 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 drying, soaking 

 in turpentine, and mounting in balsam ; the 

 same may be done with petals, sepals, &c. 

 The leaves of many water-plants, such as of 

 Vallisneria, Anacharis, Ceratophyllum, Hot- 

 tonia, &c., are very favourable for the ob- 

 servation of the rotation of the cell-sap (see 

 ROTATION). They are of very simple cel- 

 lular structure, having no epidermis, sto- 

 mata, or fibro-vascular ribs. 



Leaves also afford a large field for inter- 

 esting study to the microscopist, in the 

 examination of the colouring-matters and 

 secretions in the cells, especially during the 

 autumnal changes, of the development, &c., 

 and moreover in the investigation of the 

 parasitic Fungi which so frequently attack 

 them both in the living and the decaying 

 state. 



LECAN'ORA, Ach. A genus of Le- 

 canorei (Lichenaceous Lichens), the species 

 growing chiefly on rocks, stones, and earth. 

 Thalluscrustaceous, granular, rarely radiate ; 

 apothecia lecanorine ; paraphyses distinct ; 

 thecae either eight-spored or polysporous; 

 spores simple. 



BIBL. Hook. Br. Flor. ii. pt. 1 ; Engl. Sot. 

 pi. 940; Leighton, Lich. 1879. 



LECID'EA, Ach. A genus of Lecideinei 

 (Lichenaceous 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. geograpliica, growing on subalpine 

 recks, is a rejnarkable species. 



BIBL. Hook. Br. Fl. ii. pt. 1. 177 ; Engl. 

 Bot.pl. 24o, &c. ; Leighton, Lich. 240. 



LECIDEI'NEL A tribe of Lichenacei, 

 containing the genera Leddea, Odontotrema, 

 and Schizoxylon. 



BIBL. Leighton, Lich. Fl. 240. 



LECYTH'EA, Le>. See UREDIXET. 



LEECH. Two species of the genus Hi- 

 rudo, which belongs to the class Annulata, 

 are used for medicinal purposes, viz. H. me- 

 dicinalis, in which the ventral surface is 

 greenish, with black spots ; and //. offid- 

 nalis, in which these spots are absent. 



The structure of the mouth of the species 

 of Hiwdo is curious. The mouth is trian- 

 gular (PI. 22. fig. 25), and placed in the 

 middle of the anterior sucker. Each of its 

 three sides is furnished with a semicircular 

 jaw, of cartilaginous consistence (fig. 26, 

 side view ; fig. 27, view from above), upon 

 the convex margin of which are placed a 

 large number of partly calcareous teeth 

 (fig. 26 b) arranged in a row. The teeth 

 (fig. 28, a side view, b view from above) 

 are flattened, somewhat triangular, and ex- 

 cavated at the base, so as to exhibit two 

 short prongs (d). They are placed trans- 

 versely upon the jaws, which are moved by 

 powerful muscles, and thus produce the 

 well-known wounds. And this cross di- 

 rection of the teeth is probably the cause of 

 the troublesome bleeding accompanying the 

 bite of a leech, in consequence of the 

 amount of laceration necessarily connected 

 with it. 



The species of Hirudo have ten minute 

 eyes, arranged in the form of a horseshoe 

 at the upper part of the anterior sucker. 



The ova of leeches are deposited in a kind 

 of cocoon, composed of triangular fibres, 

 branched and interwoven so as to somewhat 

 resemble a sponge, as which one of them 

 was formerly described. 



BIBL. Bnghtwell, Ann. N. H. 1842, ix. 

 11 ; Brandt and Ratzeburg, Mediz. Zool. ii. ; 

 Johnson. Medicinal Leech ; Moquin-Tandon, 

 Monog. Hirudinees ; Savigny, Descript. de 

 TEgypte^TU.. ; Audouinand Milne-Edwards, 

 Ann. Sc. Nat. 1823, 27-30 ; R. Jones, Outl. 

 of An. Kingdom ; Gervais and Van Beneden, 

 Zool. Med. ; Schultze, Zeits. iviss. Zool. xii. 

 1862; Leuckart, Mensch. Parasit. ; Gratiolet, 

 Ann. Sd. Nat. iv. 17 ; Lankester, Qu. M. 

 Jn. 1880, xx. 307. 



LEIBLEI'NIA, Endl. A genus of ma- 

 rine plants, placed among the Ectocarpaceze 

 by Endlicher, and among Oscillatoriacea3 

 (Confervoid Algae) by Kiitzing, who includes 



