EPITHELIUM. 



[ 241 ] 



equisetacej:. 



EPITHELIUM, OF Plants. See Epi- 

 dermis, of Plants. 



EPITHEMIA, Brebisson.— A genus of 

 Diatomaceae. 



Char. Frustules single, attached by a part 

 of the surface to other bodies ; valves with 

 transverse or slightly radiant striae, some of 

 them not resolvable into dots. 



Frustules prismatic, quadi-angular, mostly 

 curved, sometimes slightly undulating: in the 

 side\'iew; one face of front ^dew (that by which 

 they are attached) flat or concave, the other 

 convex and broader than the former, so that 

 the transverse section forms a trapezoid. 

 Between, or corresp.^nding with the trans- 

 verse striae (canaliculi, Smith), not resolvable 

 into dots, are often transverse rows of dots 

 or depressions. 



The species are numerous. Aquatic and 

 marine. Conjugation has been observed in 

 three of them. 



E. turgida {Eunotia turgida, Ehr.) (PI. 12. 

 fig. 32: a, side view; b, front view). Front 

 \iew oblong, slightly dilated towards the 

 middle ; side view somewhat convex, gradu- 

 ally attenuated towards the very obtuse ends. 

 Aquatic; length 1-240". In conjugation, 

 PL 6. fig. 6, a, b, c, d, e. 



E. gibba. Straight ; inflated in the mid- 

 dle on each side in front view; side view 

 gibbous in the middle on one side, ends 

 rounded, veiT obtuse, striae transverse ; aqua- 

 tic; length 1-1-40". 



BiBL. Kiitzing, Bacillar. p. 33, and Sp. 

 Alg. p. 1 ; Smith, Brit, Diatom, i. p. 13. 



EPOCHXIUM, Lk.— A genus of Sepe- 

 doniei (Hyphomycetous Fungi), forming a 

 stratum over larger fungi or dead twigs, 

 consisting of a mycelium of irregularly 

 branched and anastomosing filaments, which 

 bear on short lateral branchlets oblong or 

 globular, septate spores, which soon fall ofi' 

 and lie among the mvcehum-threads. 



E. fungorum is very common, forming 

 a dark green stratum over Thelephorce ; 

 E. macrosporoideum was found by Mr. 

 Berkeley on a dead twig, apparently of red 

 cm*rant. 



BiBL. Berk, in Brit. Flora, vol. ii. pt. 2. 

 p. 352, Ann. Nat. Hist. i. p. 263. pi. 8. fig. 

 14. 



EQUISETACEJE and EQUISETUM.— 

 This is a very distinctly characterized family 

 of Flowerless Plants, consisting of a single 

 genus, theEquiseta, or Horse-tails, which are 

 immediately recognized, when one species is 

 known, by the peculiar aspect and habit of 

 growth. The Equiseta are found in damp 



Fig. 205. 



or wet places under the form of erect, simple 

 or branched, green or dull brown stems, ap- 

 parently devoid of leaves, jointed at short 

 intervals, and furnished with a short mem- 

 branous sheath, toothed at its free margin, 

 at each joint ; where branches exist, they 

 are sent ofi" in circles at the joints ; and the 

 branches themselves, also jointed, sometimes 

 send ofi^ similar circles of secondary branches. 

 The stems and branches are alike tubular, 

 and present in almost all cases a rather 

 coarsely (perpendicularly) streaked surface. 

 The stems appearing above ground are shoots 

 from a creeping underground stem (fig. 205), 

 which difi'ers fi'om the erect 

 stems inbeing of a deep brown 

 colour and solid, in giving ofi' 

 root-fibrils, and sometimes 

 in being covered with hairs. 

 The erect stems are either 

 barren or fertile; in the 

 barren stems the joints be- 

 come gradually thinner up- 

 wards from a certain point, 

 at last tapering ofi' to an ob- 

 tuse apex; the fertile stems 

 bear a kind of club-shaped 

 head, resembling in some 

 degree the male cones of 

 Coniferous trees, or more 

 particularlv those of some 

 Cycads (fig. 205). These 

 club-shaped bodies are the 

 fi'uits or heads of sporanges. 

 The creeping underground ^^^,,^^^^ 

 stem or rhizome branches 

 on any or all sides, but the 

 branches do not all rise as 

 erect stems or shafts ; some grow out under- 

 ground, and their joints become swollen 

 into globular or spindle-shaped tubers, some- 

 times in a long row of successive joints, so as 

 to form a necklace-shaped body, and these 

 tubers orclinarily break away from each other 

 and from the parent-stem, each to form a 

 new plant. 



The anatomical structm'e of the rhizome 

 and shafts presents some interesting points. 

 In the solid rhizome the centre is occupied 

 by cellular tissue of tolerably strong texture ; 

 outside this, as seen in a cross section, stands 

 a circle of air-canals, each sun-ounded by a 

 ring of vascular bundles ; next comes a com- 

 plete cucle of vascular bundles composed 

 almost wholly of annular ducts ; between 

 this vascular ring and the outside lies pa- 

 renchyma like that in the centre, traversed 

 by another concentric circle of air-canals, 



R 



arvense. 



One-half of 

 nat. size. 



