CHAPTER Vm (Part 1)

CHAPTER Vm STORAGE TISSUE Most drug plants contain storage products because they are collected at a period of the year when the plant is storing, or has stored, reserve products. These products are stored in a number of characteristic ways and in different types of tissue. The most important of the different types of storage tissue that occurs in plants are the storage cells, the storage cavities, and the storage walls. STORAGE CELLS Several different types of cells function as storage tissue. These cells, which are given in the order of their importance, are parenchyma, crystal cells, medullary rays, stone cells, wood fibres, bast fibres, and epidermal and hypodermal cells. CORTICAL PARENCHYMA Cortical parenchyma of biennial rhizomes, bulbs, roots, and the parenchyma of the endosperm of seeds store most of the reserve economic food products of the higher plants. Pith parenchyma of sarsaparilla root (Plate 65, Fig. 4) and the pith parenchyma of the rhizome of memspermun, like the pith parenchyma of most plants, function as storage cells. WOOD PARENCHYMA W6od parenchyma, particularly of the older wood, function as storage tissue. The wood parenchyma of quassia, like the wood parenchyma of most woods, contain stored products. In some cases the wood parenchyma contain starch, in others crys- tals, and in others coloring matter, etc. In many plants, however, the parenchyma cells contain crystals. The parenchyma cells of rhubarb contain rosette 173 I. Stone cells with starch of Ceylon cinnamon (Cinnamomiim zeylaniatm, Nees.). a. Stone cells with solitary crystals of calumba root OaUorhita palmata, [Lam.j Miers). 3. Parenchyma cells, with starch of cascarilla bark (Croion dulrria, [L,] Benn.). 4. t'urtlcal parenchyma with starch of sarsa- parilla root (Smiiax officinalis, Kiinth). 5. Cortical parenchyma, with starch of leptamlra rhixome {Lepiandra virginica, |L.] Nutt.). 6. Crystal cells, with solitary crystals of quebracho bark (Schlechtendal). 7. Bast 6bre of black- berry root with starch iRuhtis ainrifolius, Pursh.). Mucilage and Rbsin I. Cross-section of elm bark iUlmus fuiva, Michaux] showing twocavitiea Riled with partially swollen mucilage. J. Mucilage mass from sassafras slera bark (Sassafras variifolium, L.). ,V Mucilage mass from elm bark. 4. Renn mass from white pine bark (Finns Urnbiis, L.). i 176 HISTOLOGY OF MEDICINAL PLANTS crystals, while the parenchyma cells of the cortex of sarsaparilla and false unicorn root contain bundles of raphides. In every case observed the raphides are surrounded by mucilage. This is true of squills, sarsaparilla, false unicorn, etc. When cells with raphides and mucilage are moimted in a mixture of alcohol, glycerine, and water, the mucilage first swells and finally dis- appears. STORAGE CAVITIES Particular attention should be given to storage cavities whenever they occur in plants, for the reason that they are usually filled with storage products, and for the added reason that storage cavities are not conmion to all plants. Storage cavities occur in roots, stems, leaves, flowers, fruits, and seeds. CRYSTAL CAVITIES Characteristic crystal cavities occur in many plants. Such a cavity containing a bundle of raphides is shown in the cross- section of skimk cabbage leaf (Plate 67). SECRETION CAVITIES In white pine bark there are a great number of secretion cavities which are partially or completely filled with oleoresin. In the cross-sections of white pine bark the secretion cavities are very conspicuous, and they vary greatly in size. This variation is due, first, to the age of the cavity, the more re- cently formed cavities being smaller; and secondly, to the nature of the section, which will be longer in longitudinal section, which will be through the length of the secretion cavity, and shorter on transverse section. Such a section shows the width of the secretion cavity. Characteristic mucilage cavides occur in sassafras root, stem bark, elm bark (Plate 66, Fig. i), marshmallow root, etc. These cavities form a conspicuous feature of the cross-section of these plants. The presence or absence of mucilage cavities in a bark should be carefully noted. LATEX CAVITIES The latex tube cavities are characteristic in the plants in which they occur. These cavities as explained under latex tubes are very irregular in outline. Cross-Section of Skunk-cabbacb Leat (Symploearput ftelidut, [L.] Nutt.) I. Crystal cavity. a. Bundle of raphides. 178 HISTOLOGY OF MEDICIXAL PLANTS OIL CA-ITY Canella alba contains an oil cavity resembling in tonn tbe mucilage ca\ity of ehn bark. Secretion cavities occur in most of the umbelliferous fruits. For each fruit there is a more or less constant number of cavities. Anise has twentv or more, fennel usually has six ca\ities. and parsley has six ca\ities. In poison hemlock fruits there are no secretion ca\ities. In certain cases, however, the number of secretion ca'ities can be made to -ar-. This was proved by the author in the case of celer' seed. He foimd that cultivated celer- seed, from which stalks are grown, contains six oil ca\ities (Plate 122, Fig. 2), while wild celerj- seed t Plate 102, Fig. i), grown for its medicinal value, alwavs contains more than six ca\ities. Most of the wild celer' seeds contain twelve caxities. Many leaves contain cavities for storing secreted products. Such storage cavities occiu" in fragrant goldenrod, buchu, thyme, savary, etc. The leaves in which such ca\ities occur are designated as pelludd-pimctate leaves. Such leaves wiD, when held be- tween the eye and the source of light, exhibit numerous roimded translucent spots, or storage ca\ities. GLANDULAR HAIRS The glandular hair of peppermint (Plate 60, Fig. 3) and other mints consists of eight secretion cells, arranged aroimd a central cavity and an outer wall which is free from the secretion cells. This outer wall becomes greatly distended when the secretion cells are active, and the sp)ace between the secretion cells and the wall serves as the storage place for the oil. "WTien the mints are collected and dried, the oil remains in the storage cavity for a long time. STONE CELLS The stone cells of the different cinnamons (Plate 65, Fig. i) store starch grains; these grains often completely fill the stone cells. The yellow stone cells of calumba root (Plate 65, Fig. 2) usually contain four prisms of calcium oxalate, which may be nearly uniform or very unequal in size. STORAGE TISSUE 179 BAST FIBRES The bast fibres of the different rubus species (Plate 65, Fig. 7) contain starch. The medullary rays of quassia (Plate 107, Fig. 2) contain starch; while the medullary rays of canella alba contain rosette crystals. In a cross-section of canella alba (Plate 81, Fig. 3) the crystals form parallel radiating lines which, upon closer examination, are seen to be medullary rays, in each cell of which a crystal usually occurs. The epidermal and hypodermal cells of leaves serve as water-storage tissue. These cells usually appear empty in a section. The barks of many plants — Le.y quebracho, witch-hazel, cascara, frangula, the leaves of senna and coca, and the root of licorice — contain munerous crystals. These crystals occur in special storage cells — crystal cells (Plate 65, Fig. 6) — ^which usually form a completely enveloping layer around the bast fibres. These cells are usually the smallest cells of the plant in which they, occur, and with but few exceptions each cell contains but a single crystal. The epidermal cells of senna leaves and the epidermal cells of mustard are filled with mucilage; the walls even consist of mucilage. Such cells are always diagnostic in powders. STORAGE WALLS Storage walls (Plates 68 and 69) occur in colchicum seed, saw palmetto seed, areca nut, nux vomica, and Saint Ignatius's bean. In each of these seeds the walls are strongly and char- acteristically thickened and pitted. In no two plants are they alike, and in each plant they are important diagnostic characters. Storage cell walls consist of reserve cellulose, a form of cellulose which is rendered soluble by ferments, and utilized as food during the growth of the seed. Reserve cellulose is hard, bony, and of a waxy lustre when dry. Upon boiling in water the walls swell and become soft. The structure of the reserve cellulose varies greatly in the different seeds in which it occurs in the thickness of the walls and in the number and character of the pores. Reserve Cellulose sermlala, [Michaux] Hoolc, f.)> Saw palmetto (Sc Areca nut (Areca caltchu, L.). Colchicum seed {Cokhicum aiilvmnale, L.). 4. Porous side wall. ■B. Cell cavity above the ude wall. Resbkve Cellulose I. Endosperm of nux vomica {Strychttos ntc 3. Endosperm of St. Ignatia bean {Strychnc vomica, h.). ipuMi, Berg.)' CHAPTER Dl CELL CONTEXTS Tbc oeH ccctcc:* ge the ptiz.i are 'fhriQed into two groups: rR- orzazic -icil cccr^^^z inc secccclv. izorzmic cdl cixitents. The mpmk .oeC :::c. len^ bo-'fe pi.L5Cifs. starch grains. rTage. izi'i.r' suzir. rc<cer:>if=^ ^^jlcfidsw ghiooddes. tannin. CHLOROPHTLL Tlie cfaloropiasts of the hfzrer plants are green, and they vary sotnevhat in sze. b^i they have a amilar structure and form* Chlorof^asts are niostly o:L in loo^tudinal view and rounded in CTOss-aectioc -ieTr. Each chlorophyll grain has an extremely thin outer will, which end*:'aes the protoplaanic substance, the green granules, a green pigment chlorophyD'. and a yellow pigment xanthophyli . Frequently the wall includes starch, ofl drops, and protein cr^-5taI5. Chlorc^lasts are arranged either in a regular perq[>heral manner along the walls, or they are di£Fused throu^out the protoplast. The palisade cells of most lea'es are packed with chlorophyll grains. In the mesophyll cells the chlorophyll grains are not so numerous, and the' are arranged peripherally around the innermost part of the wall. Chloroplasts multiply by fission — that is, each chloroplast dix-ides into two equal halves, each of which devel<^ into a normal chloroplast. Chlorophyll occurs in the palisade, spongy parenchyma, and guard cells of the leaf; in the collench>ina and parenchyma of the cortex of the stems of herbs and of young woody stems, and, under certain conditions, in rhizomes and roots exposed to light. Almost without exception yoimg seeds and fruits have chlorophyll. 182 CELL CONTENTS 183 In powdered leaves, stems, etc., the chlorophyll grains occur in the cells as greenish, more or less structureless masses. Yet cells with chlorophyll are readily distinguished from cells with other cell contents. In witch-hazel leaf the chlorophyll grains appear brownish in color. Powdered leaves and herbs are readily distinguished from bark, wood, root, and flower powders. Leaves and the stems of herbs are of a bright-green color. With the exception of the guard cells, the chloroplasts occur one or more layers below the epidermis; but, owing to the trans- lucent nature of the outer walls of these cells, the outer cells of leaves and stems appear green. Wild cherry, sweet birch, and, in fact, most trees witn smooth barks have chloroplasts in several of the outer layers of the cortical parenchyma. When the thin outer bark is removed from these plants, the underlying layers are seen to be of a bright-green color. LEUCOPLASTIDS LeucoplastidSi or colorless plastids, occur in the imderground portions of the plant; they may, when these organs in which they occur are exposed to light, change to chloroplastids. Leucoplasts are the builders of starch grains. They take the chemical substance starch and build or mould it into starch grains, storage starch, or reserve starch. Other characteristic chromoplasts found in plants are yellow and red. Yellow chromoplasts occur in carrot root and nas- turtiimi flower petals. Red plastids occur in the ripe fruit of capsicum. STARCH GRAINS The chemical substance starch (CeHioOs) is formed in chloro- plasts. The starch thus formed is removed from the chloro- plasts to other parts of the plant because it is the function of the chloroplasts to manufacture and not to store starch. The starch formed by the chloroplasts is acted upon by a ferment which adds one molecule of water to CeHwOs, thus forming sugar CeHisOe. This sugar is readily soluble in the 184 HISTOLOGY OF MEDICINAL PLANTS cell sap, and is conducted to all parts of the plant. The sugar not utilized in cell metabolism is stored away in the form of reserve starch or starch grains by colorless plastids or amyloplasts. The amyloplasts change the sugar into starch by extracting a molecule of water. This structureless material (starch) is then formed by the amyloplast into starch grains having a definite and characteristic form and structure. Starch grains vary greatly in diflFerent species of plants, owing probably to the variation of the chemical composition, density, etc., of the protoplast, and to the environmental con- ditions under which the plant is growing. OCCURRENCE Starch grains are simple, compound, or aggregate. Simple starch grains may occur as isolated grains (Plates 70, 71, and 72), or they may be associated as in cardamon seed, white pepper, cubeb, and grains of paradise, where the simple grains stick together in masses, having the outline of the cells in which they occur. These masses are known as aggregate starch. Aggregate starch (Plate 76) varies greatly in size, form, and in the nature of the starch grains forming the aggregations. Compound starch grains may be composed of two or more parts, and they are designated as 2, 3, 4, 5, etc., compound (Plate 7s). The parts of a compound grain may be of equal size (Plate 75 1 Fig. 4), or they may be of unequal size (Plate 75, Fig. 2). In most powders large numbers of the parts of the com- pound grains become separated. The part in contact with other grains shows plane surfaces, while the external part of the grain has a curved surface. There will be one plane and one curved surface if the grain is a half of a two-compound grain; two plane and one curved surface if the grain is a part of a three- compound grain, etc. The simple starch grains forming the aggregations become separated during the milling process and occur singly, so that in the drugs cited above the starch grains are soUtary and aggregate. Many plants contain both simple and compound starch grains (Plate 74, Fig. 3). CELL CONTENTS 185 In some forms — e.g., belladomia root (Plate 75, Fig. 2) the compound grains are more numerous; while in sanguinaria the simple grains are more nimierous, etc. OUTLINE The outline of starch grains is made up of (i) roimded, (2) angled, and (3) roimded and angled surfaces. Starch grains with rounded surfaces may be either spherical, as in Plate 74, Fig. 3, or oblong or elongated, as in Plate 71, Fig. I. Other starches with rounded surfaces are shown on Plates 72 and 73. Angled outlined grains are common to cardamon seed, white pepper, cubebs, grains of paradise (Plate 76, Fig. 4), and to com (Plate 70, Fig. 3). The outlines of all compound grains are made up partly of plane and partly of curved surfaces. SIZE The size (greatest diameter) of starch varies greatly even in the same species, but for each plant there is a normal variation. In spherical starch grains the size of the individual grains is invariable, but in elongated starch grains and in parts of com- pound grains the size will vary according to the part of the grain measured. In zedoary starch (Plate 71, Fig. 4), for instance, the size will vary according to whether the end^ side, or surface of the starch grain is in focus. The parts of compound grains often vary greatly in size. Such a variation is shown in Plate 75, Fig. 2. HILX7M The hilum is the starting-point of the starch grain or the first part of the grain laid down by the amyloplast. The hilum will be central if formed in the middle of the amyloplast, and excentral if formed near the surface of the amyloplast. It has been shown that the developing starch grain with eccentric hilum usually extends the wall of the amyloplast if it does not actually break through the wall. Starch grains with excentral hilums are therefore longer than broad. 184 HISTOLOGY OF MEDICINAL PLANTS cell sap, and is conducted to all parts of the plant. The sugar not utilized in cell metabolism is stored away in the form of reserve starch or starch grains by colorless plastids or amyloplasts. The amyloplasts change the sugar into starch by extracting a molecule of water. This structureless material (starch) is then formed by the amyloplast into starch grains having a definite and characteristic form and structure. Starch grains vary greatly in diflFerent species of plants, owing probably to the variation of the chemical composition, density, etc., of the protoplast, and to the environmental con- ditions under which the plant is growing. OCCURRENCE Starch grains are simple, compound, or aggregate. Simple starch grains may occur as isolated grains (Plates 70, 71, and 72), or they may be associated as in cardamon seed, white pepper, cubeb, and grains of paradise, where the simple grains stick together in masses, having the outline of the cells in which they occur. These masses are known as aggregate starch. Aggregate starch (Plate 76) varies greatly in size, form, and in the nature of the starch grains forming the aggregations. Compound starch grains may be composed of two or more parts, and they are designated as 2, 3, 4, 5, etc., compound (Plate 7s). The parts of a compound grain may be of equal size (Plate 75, Fig. 4), or they may be of imequal size (Plate 75, Fig. 2). In most powders large numbers of the parts of the com- pound grains become separated. The part in contact with other grains shows plane surfaces, while the external part of the grain has a curved surface. There will be one plane and one curved surface if the grain is a half of a two-compound grain; two plane and one curved surface if the grain is a part of a three- compound grain, etc. The simple starch grains forming the aggregations become separated during the milling process and occur singly, so that in the drugs cited above the starch grains are solitary and aggregate. Many plants contain both simple and compound starch grains (Plate 74, Fig. 3). CELL CONTENTS 185 In some forms — e.g.,