In many Laminariaceae the thallus also grows regularly in thickness by division of its surface layer, adding to the subjacent permanent tissue and thus forming a secondary meristem.
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.
The passage from this tegumentary layer to the subjacent longitudinal muscular one is gradual, no membrane separating them.
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 ("true skin").
Strata of volcanic rock subjacent to the city and its environs, and constructed originally for the interment of the Christian dead.
- 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.
From the ventral surface of the collar nerve-tube numerous motor fibres may be seen passing to the subjacent musculature.
Thelyphonusassamensis d .Ventral surface of theanteriorregionof the opisthosoma, the first somite being pushed upwards and forwards so as to expose the subjacent structures.
The lava is emitted from the volcanic vent at a high temperature, but on exposure to the air it rapidly consolidates superficially, forming a crust which in many cases is soon broken up by the continued flow of the subjacent liquid lava, so that the surface becomes rugged with clinkers.
The left inner gill-plate is also snipped to show the subjacent orifices of the left renal organ x, and of the genital gland (testis or ovary) y.
It is not difficult in such compact species to distinguish between superficial cells, whose chief function is assimilation, subjacent cells charged with reserve material, and a core of tissue engaged in the convection of elaborated material from part to part.
Elkington showed that by cutting a deep drain through the clay, aided when necessary by wells or auger holes, the subjacent bed of sand or gravel in which a body of water is pent up by the clay, as in a vessel, might be tapped and the water conveyed harmlessly in the covered drain to the nearest ditch or stream.
All living, and most extinct, Echinoderms show the following features, almost certainly due to an ancestral pelmatozoic stage: - An incomplete radial symmetry, of which five is usually the dominant number, is superimposed on the secondary bilateralism, owing to the outgrowth from the mouth region of one unpaired and two paired ciliated grooves; these have a floor of nervous epithelium, and are accompanied by subjacent radial canals from the water-ring, giving off lateral podia and thus forming ambulacra, and by a perihaemal system of canals apparently growing out from coelomic cavities.
Again, the most convenient site for oil wells is the crest of an anticline or "dome," where an impervious stratum imprisons the gas and oil in a subjacent saturated layer under pressure.