CHAPTER III
MECHANICAL TISSUES
The =mechanical tissues= of the plant form the framework around which the plant body is built up. These tissues are constructed and placed in such a manner in the different organs of the plant as to meet the mechanical needs of the organ. Many underground stems and roots which are subjected to radial pressure have the hypodermal and endodermal cells arranged in the form of a non-compressible cylinder. Such an arrangement is seen in sarsaparilla root (Plate 38, Fig. 4). The mechanical tissue of the stem is arranged in the form of solid or hollow columns in order to sustain the enormous weight of the branches. In roots the mechanical tissue is combined in ropelike strands, thereby effectively resisting pulling stresses. The epidermis of leaves subjected to the tearing force of the wind has epidermal cells with greatly thickened walls, particularly at the margin of the leaf. The epidermal cells of most seeds have very thick and lignified cell walls, which effectively resist crushing forces.
The cells forming mechanical tissues are: bast fibres, wood fibres, collenchyma cells, stone cells, testa epidermal cells, and hypodermal and endodermal cells of certain plants. The walls of the cells forming mechanical tissues are thick and lignified, with the exception of the collenchyma cells and a few of the fibres. Lignified cells are as resistive to pulling and other stresses as similar sized fragments of steel. The hardness of their wall and their resistance to crushing explain the fact that they usually retain their form in powdered drugs and foods.
BAST FIBRES
One of the most important characters to be kept in mind in studying bast fibres is the structure of the wall. In fact, the author’s classification of bast fibres is based largely on wall structure. Such a classification is logical and accurate, because it is based upon permanent characters. Another character used in classifying bast fibres is the nature of the cell, whether branched or non-branched. In fact, this latter character is used to separate all bast fibres into two fundamental groups--namely, branched bast fibres and non-branched bast fibres. The third important character utilized in classifying fibres is the presence or absence of crystals.
Bast fibres are classified as follows: 1. =Crystal bearing.= 2. =Non-crystal bearing.=
The crystal-bearing fibres are divided into two classes: 1. =Of leaves.= 2. =Of barks.=
The non-crystal bearing are divided into: 1. =Branched.= 2. =Non-branched.=
The branched and non-branched are divided into four classes: 1. =Non-porous and non-striated.= 2. =Porous and non-striated.= 3. =Striated and non-porous.= 4. =Porous and striated.=
CRYSTAL-BEARING BAST FIBRES
The =crystal-bearing fibres= are composed (1) of groups of fibres, (2) of crystal cells, and (3) of crystals. In these cases the groups of fibres are large, and they are frequently completely covered by crystal cells, which may or may not contain a crystal. The crystals found on the fibres from the different plants vary considerably in size and form. As a rule, the fibres when separated are free of crystal cells and crystals. This is so because the crystal cells are exterior to the fibres, and in separating the fibres during the milling process the crystal cells are broken down and removed from the fibres. It is common, therefore, to find isolated fibres and crystals associated with the crystal-bearing fibres. The fibres which are crystal-bearing may be striated or porous, etc.; but owing to the fact that the grouping of the fibres and crystals is so characteristic, little or no attention is paid to the structure of the individual fibres.
[Illustration: PLATE 19
CRYSTAL-BEARING FIBRES OF BARKS
1. Frangula (_Rhamnus frangula_, L.). 2. Cascara sagrada (_Rhamnus purshiana_, D.C.). 3. Spanish licorice (_Glycyrrhiza glabra_, L.). 4. Witch-hazel bark (_Hamamelis virginiana_, L.).]
=Crystal-bearing fibres= occur in the barks of frangula (Plate 19, Fig. 1); cascara sagrada (Plate 19, Fig. 2); witch-hazel (Plate 19, Fig. 4); in cocillana (Plate 20, Fig. 1); in white oak (Plate 20, Fig. 2); in quebracho (Plate 20, Fig. 3); and in Spanish licorice root (Plate 19, Fig. 3).
The crystal-bearing fibres of leaves are always associated with vessels or tracheids and with cells with chlorophyl. The presence or absence of crystal-bearing fibres in leaves should always be noted. The crystal-bearing fibres of leaves are composed of fragments of conducting cells, fibres, crystal cells, and crystals. The crystal-bearing fibres of leaves occur in larger fragments than the other parts of the leaf, because the fibres are more resistant to powdering. Having observed that a leaf has crystal-bearing fibres, in order to identify the powder it is necessary to locate one of the other diagnostic elements of the leaf--as the papillæ of coca (Plate 21, Fig. 1), or the hair of senna (Plate 21, Fig. 3), or the vessels in eucalyptus (Plate 21, Fig. 2).
=Branched bast fibres= occur in only a few of the medicinal plants, notable examples being tonga root and sassafras root. Occasionally one is found in mezereum bark.
The bast fibre of tonga root (Plate 22, Fig. 2) often has seven branches, but four- and five-branched forms are more common. The walls are non-porous, non-striated, and nearly white.
The bast fibre of sassafras (Plate 22, Fig. 1) has thick, non-porous, and non-striated walls, and the branching occurs usually at one end only of the fibre. Most of the bast fibres of sassafras root are non-branched.
POROUS AND STRIATED BAST FIBRES
=Porous and striated= walled bast fibres occur in blackberry bark of root, wild-cherry bark, and in cinchona bark.
The fibres of blackberry root bark (Plate 23, Fig. 1) have distinctly porous and striated walls; the cavity, which is usually greater than the diameter of the wall, contains starch. These fibres usually occur as fragments.
In wild-cherry bark (Plate 23, Fig. 2) the fibre has short, thick, unequally thickened walls, which are porous and striated. Most of the fibres are unbroken.
[Illustration: PLATE 20
CRYSTAL-BEARING FIBRES OF BARKS
1. Cocillana (_Guarea rusbyi_, [Britton] Rusby). 2. White oak (_Quercus alba_, L.) 3. Quebracho (_Aspidosperma quebracho-blanco_, Schlechtendal).]
[Illustration: PLATE 21
CRYSTAL-BEARING FIBRES OF LEAVES
1. Coca leaf (_Erythroxylon coca_, Lam.). 2. Eucalyptus leaf (_Eucalyptus globulus_, Labill). 3. Senna leaf (_Cassia angustifolia_, Vahl.).]
[Illustration: PLATE 22
BRANCHED BAST FIBRES
1. Sassafras root bark (_Sassafras variifolium_, [Salisb.] Kuntze). 2. Tonga root.]
Yellow cinchona bark (Plate 23, Fig. 3) has very thick, prominently striated porous-walled fibres, with either blunt or pointed ends. The cavity is narrow, and the pores are simple or branched.
POROUS AND NON-STRIATED BAST FIBRES
=Porous and non-striated= bast fibres occur in marshmallow root and echinacea root.
The fibres of marshmallow (Plate 24, Fig. 3) usually occur in fragments. The walls have simple pores, and the diameter of the cell cavity is very wide; the pores on the upper or lower wall are circular or oval in outline (end view).
The bast fibres of echinacea root (Plate 24, Fig. 4) are seldom broken; the walls are yellow, the pores are simple and numerous. The edges and surface of the fibres are frequently covered with a black intercellular substance.
NON-POROUS AND STRIATED BAST FIBRES
=Non-porous and striated= bast fibres occur in elm bark, stillingia root, and cundurango bark. The bast fibres of elm bark (Plate 25, Fig. 1) occur in broken, curved, or twisted fragments. The central cavity is very small, and the walls are longitudinally striated.
In powdered stillingia root (Plate 25, Fig. 2) the bast fibres are broken, and the wall is very thick and longitudinally striated. The central cavity is small and usually not visible. Bast fibres of cundurango (Plate 25, Fig. 3) are broken in the powder. The cavity is very narrow, and the striations are arranged spirally, less frequently transversely.
NON-POROUS AND NON-STRIATED BAST FIBRES
=Non-porous and non-striated= walled bast fibres occur in mezereum bark, in Ceylon cinnamon, in sassafras root bark, and in soap bark.
The simplest non-porous and non-striated walled bast fibres are found in mezereum bark (Plate 26, Fig. 4). The individual fibre is very long. It often measures over three millimeters in length, so that in the powder the fibre is usually broken. The wall is non-lignified, white, non-porous, and of uniform diameter.
[Illustration: PLATE 23
POROUS AND STRIATED BAST FIBRES
1. Blackberry root (_Rubus cuneifolius_, Pursh.). 2. Wild cherry (_Prunus serotina_, Ehrh.). 3. Yellow cinchona (_Cinchona species_).]
[Illustration: PLATE 24
POROUS AND NON-STRIATED BAST FIBRES
1. Sarsaparilla root (Hypoderm), (_Smilax officinalis_, Kunth). 2. Unicorn root (Endoderm). 3. Marshmallow root (_Althæa officinalis_, L.). 4. Echinacea root (_Echinacea angustifolia_, D. C.).]
[Illustration: PLATE 25
NON-POROUS AND STRIATED BAST FIBRES
1. Elm bark (_Ulmus fulva_, Michaux). 2. Stillingia root (_Stillingia sylvatica_, L.). 3. Cundurango root bark (_Marsdenia cundurango_, [Triana] Nichols).]
In Ceylon cinnamon (Plate 26, Fig. 2) the bast fibres measure up to .900 mm. in length, so that in powdering the bark the fibre is rarely broken. These bast fibres, unlike the bast fibres of mezereum, have thick, white walls and a narrow cell cavity. Both ends of the fibre taper gradually to a long, narrow point.
In Saigon cinnamon the bast fibres are not as numerous as they are in Ceylon cinnamon. The individual fibres are thicker than in Ceylon cinnamon, and the walls are yellowish and rough and the ends bluntly pointed. These fibres are rarely ever free from adhering fragments of parenchyma tissue.
In sassafras root bark (Plate 26, Fig. 3) the fibre has one nearly straight side--the side in contact with the other bast fibres--and an outer side with a wavy outline, caused by the fibre’s pressing against parenchyma cells, the point of highest elevation being the point of the fibre’s growth into the intercellular space between two cells. The outer part of the wall tapers gradually at either end to a sharp point. The walls are white, thick, and non-porous.
In soap bark (Plate 26, Fig. 1) the bast fibres have thick, white, wavy walls and a narrow cavity. One end of the cell is frequently somewhat blunt while the opposite end is slightly tapering.
The branched stone cells of wild-cherry bark have three or more branches. The pores are small and usually non-branched, and the striations are very fine and difficult to see unless the iris diaphragm is nearly closed. The central cavity is very narrow and frequently contains brown tannin.
The branched stone cells of hemlock bark are very large; the walls are white and distinctly porous bordering on the cell cavity, which contains bright reddish-brown masses of tannin.
In cross-section bast fibres occur singly or isolated, as in Saigon cinnamon (Plate 34, Fig. 1); or in groups, as in menispermum (Plate 27, Figs. 1 and 2); or in the form of continuous bands, as in buchu stem (Plate 100, Fig. 5).
Bast fibres are seen in longitudinal view in powdered drugs. The cell cavity shows throughout the length of the fibre. This cavity differs greatly in different fibres. In soap bark (Plate 26, Fig. 1) there is scarcely any cell cavity, while in mezereum bark (Plate 26, Fig. 4) the cell cavity is very large.
[Illustration: PLATE 26
NON-POROUS AND NON-STRIATED BAST FIBRES
1. Soap bark (_Quillaja saponaria_, Molina). 2. Ceylon cinnamon bark (_Cinnamomum zeylanicum_, Nees). 3. Sassafras root bark (_Sassafras variifolium_, [Salisb.] Kuntze). 4. Mezereum bark (_Daphne mezereum_, L.).]
[Illustration: PLATE 27
GROUPS OF BAST FIBRES
1. Menispermum rhizome (_Menispermum canadensis_, L.). 2. Althea root (_Althæa officinalis_, L.) showing two groups of bast fibres.]
The pores, which are absent in many drugs, are, when present, either simple, as in echinacea root (Plate 24, Fig. 4), or they are branched, as in yellow cinchona (Plate 23, Fig. 3).
In each of the above fibres the length and width of the fibre are shown. The fibres also have pores of variable length. Such a variation is common to most fibres with pores. That part of the wall immediately over or below the cell cavity shows the end view or diameter of the pore, as in the fibre of marshmallow root (Plate 24, Fig. 3). As a rule, however, the pores show indistinctly on the upper and lower wall.
OCCURRENCE IN POWDERED DRUGS
In powdered drugs bast fibres occur singly or in groups. The individual fibres may be broken, as in mezereum and elm bark, or they may be entire, as in Ceylon cinnamon and in sassafras bark (Plate 26, Figs. 2 and 3).
The lignified walls of bast fibres are colored red by a solution of phlorogucin and hydrochloric acid, and the walls are stained yellow by aniline chloride.
In fact, few of the fibres found in individual plants occur in a broken condition.
Isolated bast fibres are circular in outline. Bast fibres, when forming part of a bundle, have angled outlines when they are completely surrounded by other bast fibres; but when they occur on the outer part of the bundle, and when in contact with parenchyma or other cortical cells, they are partly angled and partly undulated in outline.
In the bast fibres the pores are placed at right angles to the length of the fibre. The side walls show the length of the pore (Plate 24, Fig. 3); while the upper or lower wall shows the outline, which is circular, and the pore, which is very minute.
Most bast fibres have no cell contents. In some cases, however, starch occurs, as in the bast fibres of rubus.
The color of the bast fibres varies, being colorless, as in Ceylon cinnamon; or yellowish-white, as in echinacea; or bright yellow, as in bayberry bark.
Bast fibres retain their living-cell contents until fully developed; then they die and function largely in a mechanical way.
The walls of bast fibres are composed of cellulose or of lignin. Most of the bast fibres occurring in the medicinal plants give a strong lignin reaction.
WOOD FIBRES
=Wood fibres= always occur in cross-sections associated with vessels and wood parenchyma, from which they are distinguished by their thicker walls, smaller diameter, and by the nature of the pores, which are usually oblique and fewer in number than the pores in the walls of wood parenchyma, and different in form from the pores of vessels.
The wood fibre on cross-section (Plate 105, Fig. 4) shows an angled outline, except in the case of the fibres bordering the pith-parenchyma, etc., in which case they are rounded on their outer surface, but angled at the points in contact with other fibres. The pore of wood fibres is one of the main characteristics which enable one to distinguish the wood fibres from bast fibres.
The pores are slanting or strongly oblique (Plate 28, Fig. 2), and they show for their entire length on the broadest part of the wall--_i.e._, the upper or the lower surface--while in the side wall they are oblique; but they are not so distinct as they are on the broad part of the wall.
Frequently the pores appear crossed when the upper and the lower wall are in focus, because the pores are spirally arranged, and the pore on the under wall throws a shadow across the pore on the upper wall, or _vice versa_.
Wood fibres always occur in a broken condition (Plate 28, Fig. 1) in powdered drugs. These broken fibres usually occur both singly and in groups in a given powder.
The color of wood fibres varies greatly in the different medicinal woods. Fragments of wood are usually adhering to witch-hazel, black haw, and other medicinal barks. In each of these cases the wood fibres are nearly colorless. In barberry bark adhering fragments of wood and the individual fibres are greenish-yellow. The wood fibres of santalum album are whitish-brown; of quassia, whitish-yellow; of logwood and santalum rubrum, red.
[Illustration: PLATE 28
WOOD FIBRES
1. White sandalwood (_Santalum album_, L.). 2. Quassia wood (_Picræna excelsa_, [Swartz] Lindl.). 3. Logwood with crystals (_Hæmatoxylon campechianum_, L.). 4. Black haw root (_Viburnum prunifolium_, L.).]
Some wood fibres function as storage cells. In quassia the wood fibres frequently contain storage starch. The wood fibres of logwood and red saunders contain coloring substances, which are partially in the cell cavity and partially in the cell wall.
The walls of wood are composed largely of lignin.
COLLENCHYMA CELLS
=Collenchyma cells= form the principal medicinal tissue of stems of herbs, petioles of leaves, etc. In certain herbs the collenchyma forms several of the outer layers of the cortex of the stem. In motherwort, horehound, and in catnip the collenchyma cells occur chiefly at the angles of the stem. In motherwort (Plate 29, Fig. B) there are twelve bundles, one large bundle at each of the four angles, and two small bundles, one on either side of the large bundle. In catnip (Plate 29, Fig. A) there are four large masses, one at each angle of the stem.
Collenchyma cells differ from parenchyma cells in a number of ways: first, the cell cavity is smaller; secondly, the walls are thicker, the greater amount of thickening being at the angles of the cells--that is, the part of the cell wall which is opposite the usual intercellular space of parenchyma cells, while the wall common to two adjoining cells usually remains unthickened. In horehound stem (Plate 30, Fig. 2) the thickening is so great at the angles that no intercellular space remains. In the side column of motherwort stem (Plate 30, Fig. 1) the thickening between the cells has taken place to such an extent that the cell cavities become greatly separated and arranged in parallel concentric rows.
The collenchyma of the outer angle of motherwort stem (Plate 30, Fig. 3) is greatly thickened at the angles. There are no intercellular spaces between the cells, and cell cavity is usually angled in outline instead of circular, as in the cells of horehound. In certain plants intercellular spaces occur between the cells, and the walls are striated instead of being non-striated, as in the stems of horehound, motherwort, and catnip.
[Illustration: PLATE 29
_A._ Diagrammatic sketch of the cross-section of catnip stem (_Nepeta cataria_, L.). 1. Collenchyma occurring at the four angles of the stem.
_B._ Diagrammatic sketch of the cross-section of motherwort stem (_Leonurus cardiaca_, L.). 1, 2, 3. Twelve masses of collenchyma tissue occurring at the four sides of the stem.]
[Illustration: PLATE 30
COLLENCHYMA CELLS
1. Cross-section of a side column of the collenchyma of motherwort stem (_Leonurus cardiaca_, L.).
2. Cross-section of the collenchyma of horehound stem (_Marrubium vulgare_, L.).
3. Cross-section of the collenchyma of the outer angle of motherwort stem.]
Collenchyma cells retain their living contents at maturity. Many collenchyma cells, particularly of the outer layers of bark and the collenchyma of the stems of herbs, contain chlorophyll.
The walls of collenchyma consist of cellulose.
STONE CELLS
=Stone cells=, like bast fibres, are branched or non-branched. Each group is then separated into subgroups according to wall structure (whether striated, or pitted and striated, etc.), thickness of wall and of cell cavity, color of wall and of cell contents, absence of color and of cell contents, etc.
BRANCHED STONE CELLS
=Branched stone cells= occur in a number of drugs. In witch-hazel bark (Plate 31, Fig. 2) the walls are thick, white, and very porous. In some cells the branches are of equal length; in others they are unequal. In the tea-leaf (Plate 31, Fig. 1) the walls are yellowish white and finely porous. When the lower wall is brought in focus, it shows numerous circular pits. These pits represent the pores viewed from the end. The branches frequently branch or fork.
Branched stone cells also occur in coto bark, acer spicatum, star-anise, witch-hazel leaf, hemlock, and wild-cherry barks.
Non-branched stone cells are divided into two main groups, as follows:
1. Porous and striated stone cells, and, 2. Porous and non-striated stone cells.
POROUS AND STRIATED STONE CELLS
=Porous and striated= walled stone cells occur in ruellia root, winter’s bark, bitter root, allspice, and aconite. These stone cells are shown in Plate 33, Figs. 1, 2, 3, 4, and 5.
The stone cells of ruellia root (Plate 32, Fig. 1) are greatly elongated, rectangular in form, with thick, white, strongly porous walls. The central cavity is narrow and is marked with prominent pores and striations.
The stone cells of winter’s bark (Plate 32, Fig. 2) vary from elongated to nearly isodiametric. The pores are very large, the light yellowish wall is irregularly thickened, and the central cavity is very large. The pores are prominent.
[Illustration: PLATE 31
BRANCHED STONE CELLS
1. Tea leaf (_Thea sinensis_, L.). 2. Witch-hazel bark (_Hamamelis virginiana_, L.). 3. Hemlock bark (_Tsuga canadensis_, [L.] Carr). 4. Wild-cherry bark (_Prunus serotina_, Ehrh.).]
The stone cell of bitter root (Plate 32, Fig. 3) is nearly isodiametric. The walls are yellowish white and strongly porous and striated. The central cavity is about equal to the thickness of the walls.
The stone cell of allspice (Plate 32, Fig. 4) is mostly rounded in form, and when the outer wall only is in focus it shows numerous round and elongated pores. The central cavity is filled with masses of reddish-brown tannin. The striations are very prominent.
The diagnostic stone cell of aconite (Plate 32, Fig. 5) is rectangular or square in outline; the walls are yellowish and the central cavity has a diameter many times the thickness of the wall. The side and surface view of the pores is prominent, and the striations are very fine.
POROUS AND NON-STRIATED STONE CELLS
=Porous and non-striated stone cells= occur in Ceylon cinnamon, in calumba root, in dogwood bark, in cubeb, and in echinacea root.
The diagnostic stone cells of Ceylon cinnamon (Plate 33, Fig. 1) are nearly square in outline; the walls are strongly porous and the large central cavity frequently contains starch.
The stone cells of calumba root (Plate 33, Fig. 2) vary in shape from rectangular to nearly square, and the walls are greenish yellow, unequally thickened, and strongly porous. The typical stone cells contain several prisms, usually four.
The stone cells of dogwood bark (Plate 33, Fig. 3) have thick, white walls with simple and branched pores. The central cavity frequently branches and appears black when recently mounted, owing to the presence of air.
The stone cells of cubeb (Plate 33, Fig. 4) are very small, mostly rounded in outline, with a great number of very fine simple pores which extend from the outer wall to the central cavity. The wall is yellow and very thick.
The stone cells of echinacea root (Plate 33, Fig. 5) are very irregular in form; the walls are yellowish and porous, and the central cavity is very large. A black intercellular substance is usually adhering to portions of the outer wall.
The color of the walls of the different stone cells is very variable. In Ceylon cinnamon and ruellia the walls are colorless; in zanthoxylium, light yellow; in rumex, deep yellow; in cascara sagrada, greenish yellow.
The pores of stone cells, like the pores of bast fibres, are either simple or branched, and they may or may not extend through the entire wall. Many of the shorter pores extend for only a short distance from the cell cavity.
The width of the cell cavity varies considerably in the stone cells of the different plants. In aconite (Plate 32, Fig. 5), in calumba (Plate 33, Fig. 2), and in Ceylon cinnamon (Plate 33, Fig. 1), the cell cavity is several times greater than the thickness of the cell wall.
In allspice (Plate 32, Fig. 4), in bitter root (Plate 32, Fig. 3), the diameter of the cell cavity and the thickness of the wall are about equal. In cubeb (Plate 33, Fig. 4), in ruellia (Plate 32, Fig. 1), the wall is thicker than the diameter of the cell cavity.
The cavity of many stone cells contains no characteristic cell contents. In other stone cells the cell contents are as characteristic as the stone cell. The stone cells of both Saigon and Ceylon cinnamon (Plate 33, Fig. 1) contain starch; the stone cells of calumba (Plate 33, Fig. 2) contain prisms of calcium oxalate; the stone cells of allspice and sweet-birch bark contain tannin.
In cross-sections, stone cells occur singly, as in Saigon cinnamon (Plate 34, Fig. 1), ruellia (Plate 34, Fig. 2); in groups, as in cascara sagrada (Plate 34, Fig. 3); and in continuous bands, as in Saigon cinnamon (Plate 34, Fig. 4).
In powdered drugs, stone cells, like bast fibres, occur singly, as in ruellia, calumba, etc.; or in groups, as in cascara sagrada, witch-hazel bark, etc. In most powders they occur both singly and in groups.
The individual stone cells are mostly entire, as in ruellia, calumba, allspice, echinacea, etc. In cascara sagrada many of the stone cells are broken when the closely cemented groups are torn apart in the milling process. Many of the branched stone cells of witch-hazel bark and leaf, wild cherry, etc., also occur broken in the powder.
[Illustration: PLATE 32
POROUS AND STRIATED STONE CELLS
1. Ruellia root (_Ruellia ciliosa_, Pursh.). 2. Winter’s-bark (_Drimys winteri_, Forst.). 3. Bitterroot (_Apocynum androsæmifolium_, L.). 4. Allspice (_Pimenta officinalis_, Lindl.). 5. Aconite (_Aconitum napellus_, L.).]
[Illustration: PLATE 33
POROUS AND NON-STRIATED STONE CELLS
1. Ceylon cinnamon (_cinnamomum zeylanicum_, Nees). 2. Calumba root (_Jateorhiza palmata_, [Lam.] Miers). 3. Dogwood root bark (_Cornus florida_, L.). 4. Cubeb (_Piper cubeba_, L., f.) 5. Echinacea (_Echinacea angustifolia_, D.C.).]
[Illustration: PLATE 34
1. Saigon cinnamon. 2. Ruellia root (_Ruellia ciliosa_, Pursh.). 3. Cascara sagrada (_Rhamnus purshiana_, D.C.). 4. Saigon cinnamon.]
The walls of all stone cells are composed of lignin.
The form of stone cells varies greatly; in aconite the stone cells are quadrangular; in ruellia they are rectangular; in pimenta, they are circular or oval in outline; in most stone cells they are polygonal.
The lignified walls of stone cells are stained red with a solution of phloroglucin and hydrochloric acid, and the walls are stained yellow by aniline chloride.
ENDODERMAL CELLS
The =endodermal cells= of the different plants vary greatly in form, color, structure, and composition of the wall, yet these different endodermal cells may be divided into two groups: first, thin-walled parenchyma-like cells, and secondly, thick-walled fibre-like cells. In the thin-walled endodermal cells the walls are composed of cellulose, and the cell terminations are blunt or rounded. When the drug is powdered, the cells break up into small diagnostic fragments. In the thick-walled endodermal cells, the walls are lignified and porous, and the ends of the cell are frequently pointed and resemble fibres.
Sarsaparilla root, triticum, convallaria, and aletris have thick-walled endodermal cells.
STRUCTURE OF ENDODERMAL CELLS
The endodermal cells of sarsaparilla root (Plate 35, Fig. 1) are never more than one layer in thickness. The walls are porous and of a yellowish-brown color. Alternating with the thick-walled cell is a thin-walled cell, which is frequently referred to as a passage cell.
The endodermal cells of triticum (Plate 35, Fig. 2) are yellowish, and the walls are porous and striated. There are one or two layers of cells. The cells forming the outer layer have very thin outer but thick inner walls, while the cells forming the inner layer are more uniform in thickness.
The endodermal cells of convallaria (Plate 35, Fig. 3) are yellowish white in color, and the walls are porous and striated. The outer wall of the layer of cells is thinner than the inner wall. The innermost layer of cell is more uniformly thickened.
[Illustration: PLATE 35
CROSS-SECTIONS OF ENDODERMAL CELLS OF
1. Sarsaparilla root (_Smilax officinalis_, Kunth). 2. Triticum (_Agropyron repens_, L.). 3. Convallaria (_Convallaria majalis_, L.). 4. Aletris (_Aletris farinosa_, L.).]
The endodermal cells of aletris (Plate 35, Fig. 4) are yellowish brown, slightly porous and striated. There are one or two layers of these cells, and two of the smaller cells usually occupy a space similar to that occupied by the radically elongated single cell.
On a longitudinal view, the endodermal cells of sarsaparilla triticum, convallaria, and aletris appear as follows:
Those of sarsaparilla (Plate 36, Fig. 1) are greatly elongated, the ends of the cells are blunt or slightly pointed, and the walls appear porous and striated.
Those of triticum (Plate 36, Fig. 2) are elongated, the walls are porous and striated, and the outer wall is much thinner than the inner wall. The end wall between two cells frequently appears common to the two cells.
Those of convallaria (Plate 36, Fig. 3) are elongated, and the end wall is usually blunt. The outer wall is thinner than the inner wall.
Those of aletris (Plate 36, Fig. 4) are fibre-like in appearance; the ends of the cells are pointed and the wall is strongly porous. The longitudinal view of these cells is shown in plate 36.
HYPODERMAL CELLS
=Hypodermal cells= occur in sarsaparilla root and in triticum. In the cross-section of sarsaparilla root (Plate 37, Fig. 1) the hypodermal cells are yellowish or yellowish brown. The outer wall is thicker than the inner wall, and the cell cavity is mostly rounded, and contains air. The walls are porous and finely striated. On longitudinal view, the hypodermal cells of sarsaparilla (Plate 37, Fig. 2) are greatly elongated, and the outer and side walls are thicker than the inner walls. The ends of the cells are blunt and distinct from each other.
In cross-section, the hypodermal cells of triticum (Plate 37, Fig. 3) are nearly rounded in outline, and the walls are of nearly uniform thickness. In longitudinal view (Plate 37, Fig. 4) the same cells appear parenchyma-like, and the walls between any two cells appear common to the two cells.
[Illustration: PLATE 36
LONGITUDINAL SECTIONS OF ENDODERMAL CELLS
1. Sarsaparilla root (_Smilax officinalis_, Kunth). 2. Triticum (_Agropyron repens_, L.). 3. Convallaria (_Convallaria majalis_, L.). 4. Aletris (_Aletris farinosa_, L.).]
[Illustration: PLATE 37
HYPODERMAL CELLS
1. Cross-section sarsaparilla root (_Smilax officinalis_, Kunth). 2. Longitudinal section sarsaparilla root (_Smilax officinalis_, Kunth). 3. Cross-section triticum (_Agropyron repens_, L.). 4. Longitudinal section triticum (_Agropyron repens_, L.).]
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