G, Section showing thick-walled cells of the cortex in a Brown Alga (seaweed).
This may have a radial stem-like organization, a central cell-thread giving off from every side a number of short sometimes unicellular branches, which together form a cortex round the central thread, the whole structure having a cylindrical form which only branches when one of the short cell-branches from the central thread grows out beyond the general surface and forms in its turn a new central thread, from whose cells arise new short branches.
The cells immediately subjacent to the superficial assimilating layer form a colorless, or nearly colorless, parenchymatous cortex, which acts as a food storage tissue (fig.
In a few cases the hydrom strand is continued into the cortex of the stem as a leaf-trace bundle (the anatomically demonstrable trace of the leaf in the stem).
This in several cases runs vertically downwards for some distance in the outer cortex, and ends blindlythe lower end or the whole of the trace being band-shaped or star-shaped so as to present a large surface for the absorption of water from the adjacent cortical cells.
This bundle is continued down into the cortex of the stem as a leaf-trace, and passing very slowly through the sclernchymatous external cortex and the parenchymatous, starchy internal cortex to join the central cylinder.
Besides this there is usually a living conducting tissue, sometimes differentiated as leptom, forming a mantle round the hydrom, and bounded externally by a more or less well-differentiated endodermis, abutting on an irregularly cylindrical lacuna; the latter separates the central conducting cylinder from the cortex of the seta, which, like the cortex of the gametophyte stem, is usually differentiated into an outer thick-walled stereom and an inner starchy parenchyma.
Special tissues (stereom) may be developed for this purpose in the cortex, or in immediate connection.
The cortex of a young stem is usually green, and plays a more or less important part in the assimilative function.
This lacunar system not only enables the cells of the cortex itself to respire, but also forms channels through whicF air can pass to the deeper lying tissues.
The cortex of the older stem of the root frequently acts as a reserve store-house for food which generally takes the form of starch, and it also assists largel) in providing the stereom of the plant.
Sclerenchyma may bi formed later in various positions in the cortex, according to loca needs.
Scattered single stereids or bundles of fibres are no imnrornmnn in the rnrtev of the root The innermost layer of the cortex, abutting on the central cylinder of the stem or on the bundles of the leaves, is called the jthloeoterma, and is often differentiated.
In other cases it does not differ histologically from the parenchyma of the rest of the cortex, though it is often distinguished by containing particularly abundant starch, in which case it is known as a starch sheath.
The whole cylinder is enclosed by the peculiarly differentiated innermost cell-layer of the cortex, known as the endodermis.
In the majority of ferns, at a higher level, after the stele has increased greatly in diameter, a large-celled true pith or medulla, resembling the cortex in its characters, and quite distinct from conjunctive, from which it is separated by an internal endodernlis, appears in the centre.
The centre of the S~hooo- stele is however often occupied by a large-celled pith resembling the cortex in structure, the cortex and pith ~ together being classed as ground tissue.
In some forms other gaps (perforations) appear in the vascular tube placing the pith and cortex in communication.
The inner layer of the cortex (phloeoterma) may form a well-marked endodermis, or differ in other ways from the rest of the cortex.
They can be traced upwards from any given point till they are found to pass out of the cylinder, travel through the cortex of the stem and enter a leaf.
In some cases this individualization is carried ftirther, the cortex and pith becoming continuous between the bundles which appear as isolated strands em- Aberrant bedded in a general \, L.~/ ~ Typesof ground-tissue.
Sieve-tubes with accompanying corn- diameter of the stem, the cortex sd.p~cierizedperid~sm.
2o.Laticiferous vessels from the cortex of the root Scoyzonera hispanica, tangential secf ion.
The initials of the cortex and central cylinder Whether these art always in layers which remain separate is not known, but it is certair that in many cases such layers cannot be distinguished.
Thi vascular system is connected in various ways with that of th(parent axis by the differentiation of bundle-connections across thi cortex of the latter.
Our outside and often thin and fanciful clothes are our epidermis, or false skin, which partakes not of our life, and may be stripped off here and there without fatal injury; our thicker garments, constantly worn, are our cellular integument, or cortex; but our shirts are our liber, or true bark, which cannot be removed without girdling and so destroying the man.