LEMNA. 



[ 383 ] 



LEPTDOPTERA. 



and finally breaking up into elliptical spores. 

 British genus : 



LEMANIA. Character the same as of the 

 tribe. Two species have been found in Bri- 

 tain, L. torulosa, Ag. and L.fluviatilis. They 

 always grow in clear running streams. Mr. 

 Thwaites has made some interesting obser- 

 vations on the development of these plants. 



BIBL. Hassall, Brit. Freshw. Alg. p. 68. 

 pi. 7-J Kutzing, Phyc. generates, p. 261; 

 Thwaites, Ann. Nat. Hist. 2 ser. i. p. 460. 



LEMNA, L. Duckweed. A genus of 

 aquatic Monocotyledonous plants, remark- 

 able for the simplicity of the structure, the 

 vegetative system being replaced by a mi- 

 nute leaf-like floating stem, with dependent 

 rootlets, furnished with a curious sheath 

 (pileorliize] at the end. They bear two monre- 

 cious imperfect flowers, and also propagate by 

 bulbils formed in the slits in the side of the 

 lenticular stems ; the young bulbils formed 

 in autumn sink when the parent dies, and 

 rise again in spring. Spiral vessels occur 

 abundantly in L. potyrhiza ; they are spa- 

 ringly present in the rest. 



BIBL. Hook, and Arnott, Brit. Flor. p. 

 463 ; Schleiden, Beitr. zurBotanik. p. 229 ; 

 Weddell ( Wolffia], Ann. des Sc. nat. 3 ser. 

 p. 12. 155. 



LEMON, ESSENTIAL OIL OF. This is 

 sometimes used in microscopic examination 

 of pollen and other structures, which are 

 placed in it to render them more transpa- 

 rent, it being less diagreeable and less vola- 

 tile than oil of turpentine. Glycerine may 

 often be substituted. 



LENTICELS. Structures found upon 

 the surface of young stems, especially of 

 most of the Dicotyledonous shrubs and trees. 

 They first appear on the yearling shoot as 

 little specks, of a different colour from the 

 rest of the epidermis. Towards the winter, 

 or in early spring, the epidermis splits lon- 

 gitudinally over the lenticels, which become 

 then slightly projecting papilla?, frequently 

 divided into lips, as it were, by a median 

 furrow. The surface of the papilla is now 

 brown, and it is of corky character for some 

 little distance inward. As the branch grows, 

 the lenticels become drawn out laterally, so 

 as to appear like cross striae. They are sub- 

 sequently lost sight of by the bark splitting 

 through them, as in the apple or beech, or 

 by the bark peeling off" (plane). 



Microscopic examination of sections shows 

 that they are mere cellular productions from 

 the mesophlaeum, or cellular envelope of the 

 BARK, and have no connexion with the liber 



or cambium. DeCandolle imagined they 

 were root-buds, where adventitious roots 

 might arise under favourable circumstances; 

 but this was an error. Du Petit Thouars 

 thought they were breathing pores, replacing 

 the stomates of the epidermis ; but they are 

 not pores, and many trees, such as the Coni- 

 fers, Roses, Euonymus europaus, &c., have 

 none. 



BIBL. DeCandolle, Ann. des Sc. nat. vii. 

 p. 5 (1826); Von Mohl, Vermischt. Schrift. 

 pp. 229. 233 ; Meyer, Linnaa, vii. p. 447 ; 

 Du Petit Thouars, Essais sur la Vegetation, 

 p. 20 ; Unger, Flora, 1836. ii. p. 577. 



LEOCARPUS, Lk. See DIDERMA. 



LEPADELLA, Bory. A genus of Rota- 

 toria, of the family Euchlanidota. 



Char. Eyes absent ; foot forked. 



Three species. In two of them the jaws 

 have each a single tooth; in the other, each 

 two teeth. 



L. emarginata (PI. 34. fig. 43). Carapace 

 depressed, oval, anterior portion broad, 

 emarginate at each end. Aquatic; length 

 of carapace 1-570". 



Teeth of L. ovalis, PI. 34. fig. 44. 



BIBL. Ehrenberg, In/us, p. 457. 



LEPEOPHTHIRUS, Nordm. A genus 

 of Crustacea, of the order Siphonostoma, 

 and family Caligidae. 



Char. Fourth pair of legs slender, not 

 branched, formed for walking ; thorax with 

 only two distinct joints ; frontal plates des- 

 titute of sucking disks on the under surface. 

 Six British species, found upon various ma- 

 rine fishes, as the salmon, mackerel, sole, 

 brill, turbot, &c. 



L. pectoralis (PI. 14. fig. 23). Female. 

 Carapace oval ; frontal plates small, notched 

 in the centre; antennas small; thorax as 

 long as the carapace, penultimate joint very 

 narrow, last joint nearly as long as the cara- 

 pace, almost quadrilateral and slightly lobed 

 posteriorly; abdomen short; caudal plates 

 small, terminal setae short ; sternal fork with 

 simple sharp-pointed branches; third pair 

 of foot-jaws large. Length about 1-2". 



BIBL. Baird, Brit. Entomostraca, p. 273. 



LEPIDOPTERA. An order of Insects, 

 consisting of butterflies and moths. 



Lepidopterous insects present several 

 points of interest to the microscopic ob- 

 server; among these may be mentioned 

 especially the proboscis or ANTLIA, the 

 hook connecting the wings (INSECTS, p. 359), 

 the wings themselves, and the beautiful 

 scales covering them (SCALES OF INSECTS, 

 TEST-OBJECTS). Their larvae or caterpillars 



