ELDER. 



[ 224 ] 



ELYTRA. 



to the valves ; they here mostly present the 

 appearance of cylindrical cellulose tubes, 

 closed at the ends, with a flat spiral band 

 coiled in an open spiral, adherent to the cell- 

 membrane forming the wall (PL 32. fig. 38). 

 The elaters found among the spores of Mar- 

 chantia polymorpha (PI. 32. figs. 36,37) are 

 very long, and contain a double coil, the 

 ends of the two fibres coalescing into a loop 

 at each extremity (PI. 32. fig. 37 b) ; so that 

 the entire fibre may be compared to a piece 

 of string with its ends united, and laid out 

 so as to represent two cords, side by side, 

 which are then twisted spirally round one 

 another. In Targionia the tubes are 

 sometimes branched. The spiral fibres have 

 been stated by some authors to originate 

 from the gradual accumulation of granules 

 in a spiral line upon the primary cell-wall ; 

 but this is erroneous ; their development is 

 similar to that of the spiral fibres of vessels. 

 See Hepaticace^. 



Structures apparently analogous to these 

 elaters of the Hepaticaceae occur in some of 

 the Myxogastrous Fungi, as in Trichia 

 (PI. 32. fig. 39 a), while in other genera of 

 this family filamentous bodies, either plain or 

 obscurely marked, occur. In Batarrea, also, 

 one of the PufF-balls, a kind of elater, exists 

 accompanying the spores (see Trichogas- 

 TREs). It has been stated by Schleiden 

 and Schacht that the elaters of these 

 Fungi are solid filaments with spiral ridges 

 upon them, or else flat solid ribands twisted 

 on their longitudinal axis. This statement 

 is at variance with our observations, and is 

 not borne out by the drawings given by these 

 authors themselves. Mr. Currie, while also 

 contesting Schleiden's view, states that the 

 spiral line is a ridge outside a tube, a condi- 

 tion of things unlike anything else we are 

 acquainted with in vegetables. 



The elaters of Trichia require a very high 

 power for their elucidation, an eighth or 

 twelfth, with a high eye-piece, and a good 

 light ; they may then he seen to consist of 

 tubes with spiral fibrous secondary deposits 

 upon the inside of their walls (PI. 32. fig. 40). 

 See Spiral Structures. 



BiBL. See under Equisetace^, Mar- 

 chantia, Trichia, Spiral Structures. 

 ELDER. — Sambucus niger, the common 

 Elder-tree (Caprifoliacese, Dicotyledons), is 

 remarkable for the great development of its 

 pith ; sections of this furnish very accessible 

 and convenient illustrations of vegetable 

 parenchyma. This pith is also used by 

 microscopists for cleaning their object- 



glasses ; it is extracted from the branches in 

 suitable lengths, dried and carefuUypreserved 

 from dust. The face of the objective is 

 polished with the end of one of these cylin- 

 ders of pith, and a fresh surface is obtained 

 every time it is used, by cutting off^ a thin 

 slice with a clean razor. By this means all 

 danger of scratching the lenses is avoided. 



ELYTRA. — The horny anterior pair of 

 wings of the Coleoptera ; sometimxCs called 

 wing-covers or wing-cases, because they 

 cover and protect the subjacent pair of wings 

 of these insects, when not in use. 



The elytra may be regarded as consisting 

 of an elongated, depressed fold of the inte- 

 gument, comparable to the web between the 

 fingers, or that of the bat's wing. Four 

 structures are distinguishable in them : — l,an 

 outer, firmly adherent, epidermic layer, com- 

 posed of minute cells, frequently undistin- 

 guishable, or at least only to be detected in 

 parts ; this layer is continued around the 

 margins of the elytra^ so as to cover their 

 inferior surface also, forming, 2, the inner epi- 

 dermic layer, in which the cells are statedtobe 

 less distinct, more rounded, and more closely 

 placed than those in the upper layer, hence 

 presenting a more distinctly angular form; 

 this layer is easily detached from the elytra, 

 and its surface next the body of the insect 

 is frequently furnished with a number of 

 very minute hairs, or spiniform papillae 

 directed backwards (PI. 27. fig. 2). Beneath 

 the outer epidermic layer is 3, a layer of 

 dark resinous pigment, whether contained in 

 cells or not has not been determined. 4. an 

 intermediate portion, composing the prin- 

 cipal thickness of the elytrum, representing 

 the two fused strata of the cutis, and consist- 

 ing of a number of fibres, running in different 

 directions, variously interlacing, anastomo- 

 sing and crossing, so as to form numerous 

 plates or secondary layers, many of which 

 present a fenestrated appearance ; as many 

 as sixteen of these plates have been sepa- 

 rated. 



The veins or nerves of the elytra either 

 traverse the intermediate thick layer of the 

 elytra, or run between its under surface and 

 the inner epidermic layer, to which they 

 sometimes remain adherent. See Insects. 



The structure of the elytra can only be 

 made out by macerating them for a very long 

 time in solution of caustic potash, or water. 



BiBL. Schmidt, Taylor's Scientific Me- 

 moirs, V. p. 16; Meyer, Miiller's Archiv, 

 1842, p. 12; Nicolet, ydnn. des Sc. nat. 3rd 

 ser. vii. ; and the Bibl. of Insects. 



