This consists typically of close-fitting layers of cells with completely suberized walls, intended to replace the epidermis as the external protective layer of the plant when the latter, incapable as it is of further growth after its original formation, is broken and cast off by the increase in thickness of the stem through the activity of the cambium.
The epidermis of a very large number of species bears hairs of various kinds.
In the epidermis itself (rarely), in any layer of the cortex, or in the pericycle.
- Stinging Hair of Urtica dioica, with a portion of the epidermis, and, to the right, a small bristle (X60).
Usually they are absent from the cells of the epidermis, though in some of the lower plants they are met with there also.
Many species of Thysanoptera are known to be habitually parthenogenetic. The eggs are laid on the food-plant, those females possessed of an ovipositor cutting through the epidermis and placing their eggs singly within the plant-tissues; a single female may take five or six weeks to deposit all her eggs.
In many forms its hyphae are particularly thick-walled, and may strikingly resemble the epidermis of a vascular plant.
Its most usual seat of origin in the stem is the external layer of the cortex immediately below the epidermis; in the root, the pericycle.
In favour of seeing in the lateral trunks and their branches a vascular system, is the contractility of the former, and the fact of the intrusion of the latter into the epidermis, matched among the Oligochaeta, where undoubted blood capillaries perforate the epidermis.
These hollow roots terminate blindly in the dorsal epidermis of the collar, and place the nervous layer of the latter in direct connexion with the fibres of the nerve-tube.
Doing this she bursts the epidermis of the rootlet, and her body projects into the surrounding earth.
The disease spreads by the mycelium growing ever the epidermis of the plant.
In such leaves, there are a well-marked cuticle, a thick epidermis, a thick hypodermis at least on the upper side of the leaf, well-developed palisade tissue, and a poorly developed system of air-spaces.
In Lanice conchilega the posterior series of nephridia are connected by a thick longitudinal duct, which seems to be seen in its most reduced form in Owenia, where a duct on each side runs in the epidermis, being in parts a groove, and receives one short tubular nephridium only and occupies only one segment.
Beneath the epidermis is a longitudinal layer of muscle-fibres which are separated into four distinct groups by the dorsal, ventral and lateral areas; these are occupied by a continuation of the epidermic layer; in the lateral areas run two thin-walled tubes with clear contents, which unite in the anterior part of the body and open by a pore situated on the ventral surface usually about a quarter or a third of the body length from the anterior end.
This surface layer in the typically subaerial shoot of the sporophyte in Pteridophytes and Phanerogams is known as the epidermis, though the name is restricted by some writers, on account of developmental differences, to the surface layer of the shoot of Angiosperms, and by others extended to the surface layer of the whole plant in both these groups.
Sometimes the epidermis is considerably more developed by tangential division of its cells, forming a many-layered water-tissue.
In all green plants which have a special protective epidermis, the cortex of the shoot has to perform the primitive fundamental function of carbon assimilation.
The main assimilating tissue, on the other hand, is under the upper epidermis, where it is well illuminated, and consists of oblong cells densely packed with chloroplasts and with their long axes perpendicular to the surface (palisade tissue).
C/i, epidermis; st stoma; me,, mesophyil; pal, palisade; spa, spongy tissue; Isp, inteicellular space; wi., water tissue; x, xylem; p/i, phioem; Phil, phloeoterma; sri, scierenchyma.
In the leaf-blade this sometimes aopears as a layer of thickened subepidermal cells, tht hypoderm, often also as subepidermal bundles of sclerenchymatou~ fibres, or as similar bundles extending right across the leaf from mu epidermis to the other and thus acting as struts.
This tissue remains living and is usually formed quiti early, just below the epidermis, where it provides the first periphera support for a still growing stem or petiole.
The epidermis in the stair and the surface layer of the root soon becomes differentiated froit the underlying tissue.
Throughout the Angiosperms the epidermis of the shoot originates from separate initials, which never divide tangentially, so that the young shoot is covered by a single layer of dividing cells, the dermatogen.
The branches of the stem arise by multiplication of the cells 01 the epidermis and cortex at a given spot, giving rise to a protuber ance, at the end of which an apical meristem is established.
E, epidermis; q, phellogen; 1, cells, and ~1, the pheliogen of the lenticel; k, cortical parenchyma, containing chlorophyll.
The opening and closing of the stomata is the result of variation in the turgidity 01 their guard cells, which is immediately affected by the condition of turgidity of the cells of the epidermis contiguous to them.
The only way in which their turgidity is modified is by the entry of water into them from the contiguous cells of the general epidermis and its subsequent withdrawai through the same channel.
The other type is called endctropic. The fungal filaments either penetrate the epidermis of the root, or enter it from the stem and ramify in the interior.
From the outer cortical myceliuni, again, branches pass through the epidermis and grow out in the soil, In stich cases the roots of the plants are usuall) found spreading in soils which contain a large amount of humus, or decaying vegetable matter.
The body wall consists of an epidermis which secretes a delicate cuticle and is only ciliated in Aeolosoma, and in that genus only on the under surface of the prostomium.
The epidermis contains numerous groups of sense cells; beneath the epidermis there is rarely (Kynotus) an extensive connective tissue dermis.
A further fact must be considered in deciding this question, which is the discovery of ramifying coelomic tubes, approaching close to, but not entering, the epidermis in the Polychaete Arenicola.
They are found one on each cephalic tentacle, and are simply minute open pits or depressions of the epidermis, the epidermic cells lining them being pigmented and connected with nerves (compare fig.
Special thickenings of the diffuse nervous layer of the epidermis occur in certain regions and along certain lines.
Pression of epidermis, opening downwards.
In relation to its characteristic function of protection, the epidermis, which, as above defined, consists of a single layer of cells has typically thickened and cuticularized outer walls.
In correspondence with its water-absorbing epidermis function it is not cuticularized, but remains usually thinof Root, walled; the absorbing surface is increased by its cell~
The capillaries sometimes (in many leeches and Oligochaeta) extend into the epidermis itself.
Usually the epidermis is immediately followed by the circular layer of muscles, and this by the longitudinal coat.
The clitellum consists of a thickening of the epidermis, and is of two forms among the Oligochaeta.
In the aquatic genera the epidermis comes to consist entirely of glandular cells, which are, however, arranged in a single layer.
In the earthworms, on the other hand, the epidermis becomes specialized into several layers of cells, all of which are glandular.
(as it appears) of the epidermis, and that it performs the function of a spermatheca is shown by its containing spermatozoa, or, in Stuhlmannia, a spermatophore.
We have thus the replacement of a spermatheca, corresponding to those of the remaining families of Oligochaeta, and derived, as is believed, from the epidermis, by a structure performing the same function, but derived from the mesoblastic tissues, and with a cavity which is coelom.
The nervous system is embedded in the epidermis, and the pairs of ganglia are separated as in Serpula, &c.; each pair has a longish commissure between its two ganglia.
The fungus mycelium grows between the cuticle and the epidermis, the former being ultimately ruptured by numerous short branches bearing spores (conidia) by means of which the disease is spread.
The development of these organs, which in the Protonemertine are but grooves in the epidermis, not far removed from the similar cephalic slits of many Turbellaria, reaches its height in Drepanophorus.
Externally is a thin cuticle; this covers the epidermis, which consists of a syncytium with no cell limits.
Salicyclic acid is not absorbed by the skin, but it rapidly kills the cells of the epidermis, without affecting the immediately subjacent cells of the dermis.
- At the base of the epidermis (which is in general ciliated) there is over the entire surface of the body a layer of nervefibres, occurring immediately outside the basement-membrane which separates the epidermis from the subjacent musculature.
In one family, the Ptychoderidae, the medullary tube of the collar is connected at intermediate points with the epidermis by means of a variable number of unpaired outgrowths from its dorsal wall, generally containing an axial lumen derived from and in continuity with the central canal.
Both male and female gonads consist of more or less lobulated hollow sacs connected with the epidermis by short ducts.
H, Epidermic cell-layer; mes, mesoblastic connective tissue; n, nerves; II, III, IV, V, depressions of the epidermis in each of which a cuticular lens will be formed.
The female burrows in the epidermis much as the female trap-door spider burrows in turf in order to make a nest in which to rear her young.
One chief means employed by nature in accomplishing this object is the investment of those parts of the organism liable to be attacked with an armour-like covering of epidermis, periderm, bark, &c. The grape is proof against the inroads of the yeastplant so long as the husk is intact, but on the husk being injured the yeast-plant finds its way into the interior and sets up vinous fermentation of its sugar.
The root of the French vine is attacked by the Phylloxera, but that of the American vine, whose epidermis is thicker, is protected from it.
So long as the epidermis of animals remains sound, disease germs may come in contact with it almost with impunity, but immediately on its being fissured, or a larger wound made through it, the underlying parts, the blood and soft tissues, are attacked by them.
(After de Bary.) In A several cells of the epidermis plants.
Then come the glandular surface (C), which is formed of smooth polished epidermis with numerous glands that secrete the fluid contents of the pitcher, and finally the detentive surface (D), of which the cells are produced into long and strong bristles which point A FIG.
In a second type they are situated at the ends of tracheal strands and consist of groups of richly protoplasmic cells belonging to the epidermis (as in the leaves of many ferns), or to the subjacent tissue (the commonest type in flowering plants); in this last case the cells in question are known as epithem.
Epiphytic plants and desert plants) have absorptive hairs or scales on the leaf epidermis through which rain and dew can be absorbed.
The surface layer of the root, sometimes included under tht term epidermis, is fundamentally different from the epidermis of the stem.