CHAPTER III WOODY STEMS
BUCHU STEM
The cross-section of a buchu stem (Plate C), 1.6 millimeters in diameter, shows a few of the epidermal cells modified into thick-walled, roughish, unicellular trichomes (i). The remain- ing epidermal cells have a thick, wavy outer wall (2). Beneath the epidermis are several rows of cortical parenchyma cells (3) which extend to the bast bundles and in which are found the secretory cavities with the thin- walled secretor>' cells (4). The bast fibres (5) occur in continuous bands, varying greatly in size; the walls are whitish and of variable thickness. Inside the bast fibres, the small irregular sieve cells (6) occur in groups, surroimded by the phloem parenchyma (8). The radially elongated cells of the medullary rays (7) extend outward from the xylem, increasing in number in the outer portions of the wood, and extending nearly to the bast fibres. No distinct cambium layer is visible. The conducting cells (9) occur throughout the xylem surrounded by the wood fibres and wood parenchyma (10). The latter is not very abimdant in buchu. The medullary rays border on the conducting cells and extend outward to the phloem. The pith parenchyma cells are nearly circular in outline and often show a perforated end wall when a cell happens to be cut just above or below that point.
MATURE BUCHU STEM
In Plate loi-A is shown the cork formation or secondarj' growth as seen in the older, larger buchu stems. The wav>'' epidermis (i), which is the primary epidermis and which has disappeared on many portions of the stem, has thin side walls and dark cell contents (2). Next to the epidermal cells occur several rows of peculiarly arched cork cells with thick, white outer walls (3) and reddish-brown cell contents (4). The cork
242
CROss-SEcnOH OF BcCRu Stbus (Barosma beluiina (BerK-], Barth. and Wendl.) I. Haira. 3. Wavy epidermis. 3. Cortical parenchyma. 4. SecretioD (-ells and cavity. S- Group of bast fibres. 6. Steve cells. 7. Medullary raya. H. Phloem parenchyma. 9. Vessels. 10. Wood fibres, and wood parenchyma. II. Pith parenchyma.
... . . 1 of buchu stem (Barosma beluiina [Ber^.], Barth. and
Wendl.). I, Outer wall of epidermis; a, Cellcavity of epidemialcell; 3, Wall of cork cell; 4, Cavity of cork cell; 5, Phellogen layer; 6, Divided phellogen cell changing into a cortical parenchyma cell; 7, Cortical parenchyma cell.
B. Cross-section of leptandra rhizome {Leptandra virpnica [L.|, Nutt.)- I, Parenchyma cells undergoing change in the composition of their vralls; », A break in the epidermal tissue; 3, Parenchyma cells underling diviaioa.
WOODY STEMS 245
cambium (5) is typical in form, and it has formed one or two layers of phelloderm cells (6) which have the same form as the cambium cells but with thicker walls. Next to the phelloderm occur the cortical parenchyma cells. The remaining structure of the mature stem is identical with that of Fig. 2.
POWDERED BUCHU STEM
Powdered buchu stem (Plate 102) has many striking features which make it easy of identification when mixed with buchu leaves. A few unicellular, rough, thick, white-walled trichomes (i) occur distributed throughout the field. They are straight or slightly curved and vary in length from 40 to 100 microns; in thickness at the bast they measure from 10 to 22 microns. The central cavity varies greatly, and in some trichomes seems to have disappeared entirely. The epidermal cells (2) are very characteristic, occurring singly or in groups of two or more. The cells from the older stems often appear reddish brown by transmitted light, while the epidermal cells from the younger stems appear whitish opaque (porcelain-Iike). They are usually six-sided and angular in outline. The cortical parenchyma cells (3) on transverse view have a rounded cell cavity and intercellular spaces between the walls. The double walls vary in thickness, tiie greatest thickness being about 9 microns. The {>arenchyma cells (3) on longitudinal view show square ends and often contain sphaero-crystalline masses of hesperidin. The thin-walled sieve cells and the surrounding cells are scarcely ever seen in the powder. The white-walled pointed stereomes (4) are a characteristic feature of the powder; they vary greatly in length, in diameter and in the thickness of their walls. In a number eighty powder the fibres are mostly broken. The greatest length of the unbroken fibres is 1.25 microns. The thickest wall measured 5 microns and the greatest observed width was 25 microns. The spiral reticulate and scalariform thickened conducting cells occur scattered throughout the powder. The reticulate and scalariform cells usually occur with wood fibres. It is an interesting fact that the spiral thickening in conducting cells is usually separate from the side wall and nearly always appears as indicated at 5. An occasional rosette crystal of calcium oxalate (6) is seen in the field. The wood
Powdered Buchu Stems (Barosma btiuUna (Berg.], Barth. and Wendl.).
I. Hairs, a. Epidermal cells, the larger pieces reddish-brown: the smaller aggregations white. 3. Transverse cortical parenchyma. 3'. Longitudinal cortical parenchyma with sphxro cr>'stalline masses of hesperidin. 4. Bast fibres. 5. Spiral, sclariform, and reticulate vessels, 6. Rosette crystals of rakium oxalate. 7. Wood parenchyma. 8. Pith parenchyma with porous side and end walls. 9. Wood fibres.
WOODY STEMS 247
parenchyma (7), which makes up a very small percentage of the xylem, is not readily found in the powder. The pith paren- chyma cells (8) have thick, porous side walls and perforated side walls. The wood fibres (9) usually occur in masses surrounding the conducting cells; when occurring singly, the oblique pores readily distinguish them from the bast fibres.
The diagnostic elements of powdered buchu stems are: First, trichomes; secondly, reddish-brown and white-angled epidermal cells; thirdly, the long, white bast fibres.
IV
BARKS
Barks are all obtained from dicotykdoixxis jdants. In studying barks there should be ascertained the thickness, ar- rangement, form, structure, color, and cdl contents of the cells occurring in the outer, middk, and inner barks.
The outer bark includes the cork cdls and the phellogen layer. The middle bark includes all the cells occurring between the phellogen layer and the beginning of the medullary ra*s. The inner bark includes the medullar}' ray cdls and all cells associated with them. The plan of structure of all barks is similar, but in each species of plant the structure of the bark is uniform and characteristic for the ^)ecies.
A great number of drugs consist of the bark of woody plants; for this reason the bark is considered in a separate chapter from the stem.
WHITE PINE BA&K
The cross-section of white pine bark (Plate 103) has the following structure:
Outer Bark. The periderm consists of several layers of reddish-brown cork cells (i) which are narrow, elongated, and with thin walls.
Middle Bark. The cells forming the middle bark are paren- chyma and secretion cells.
The parenchyma cells vary greatly in size, form, and thick- ness of the walls. The cells beneath the cork cells and around the secretion cells are tangentially elongated and oval in shape, while the other parenchyma cells are more irregular in shape.
The secretion cells are arranged around the schizogenous secretion cavities. The cells are tangentially elongated, and the walls, which are slightly papillate, are white.
Inner Bark. The cells forming the inner bark are medullary rays, parenchyma, sieve cells, and storage cavities.
248
Ckoss-Section of Unrossbd White Pike Bark (Pimm strobus, L.)
I . Cork cells of the epidermis. 2. Parenchyma cells filled with chlo«q)hyl. 3. Intercellular space. 4. Secretion cavity with resin. 5, Secretion cells. 6. One or more circles ot parenchyma filled with chlorophyl. 7. Parenchyma. 8. Medullary rays. 9, Sieve cells. 10. Storage cavities.
250 mSTOLOGY OF MEDICINAL PLANTS
The medullary rays form wavy lines. The medullary ray cells are radially elongated, rectangular in shape, and they con- tain granular cell contents. The sieve cells are either square or rectangular in shape. The walls are thin and white. The storage cavities are either fiUed vnth starch or with prisms and tannin.
POWDERED WHITE PINE BARK
White pine bark (Plate 104) when powdered shows the following characteristic elements:
The microscopic structure of a powdered white pine is as follows: The epidermis (i) consists of reddish-brown masses, irregular in outline. The outer parenchjmia cells are of a bright- green color, owing to the presence of chlorophyll. (The above elements are not usually found in the rossed bark.) The paren- chyma (3) with starch usually occurs in longitudinal sections accompanied with sieve cells. Often the tissue separates trans- versely, showing the medullar>' rays (4) with their granular cell contents (9) and the inner parenchyma cells filled with starch and the surrounding sieve cells.
The crystals are nearly perfect cubes and occur singly (5) or in groups (6). On the longitudinal section of the bark the crystals occur in parenchyma cells surroimded by a reddish cell content and form parallel rows which are very characteristic. The resin occurs either as white, angled fragments (7) in a water mount, or as globular mass (8) or as reddish-brown pieces (10). The starch is very abundant and is distributed through the field. The diagnostic grain is lens-shaped, with a cleft hiliun, which is nearly straight, or slightly curved, and runs parallel to the long diameter of the grain. The addition of ferric chlorid T. S. will show the presence of tannin by forming a dark coloration. The identification of the starch is facilitated by the addition of a weak Lugol's solution, which imi>arts a blue coloration to the starch grain.
The form, amount, and distribution of the cells composing the bark differ greatly in different plants.
In cramp bark the cork and phellogen cells are very large, while in cascara sagrada the phellogen and the cork cells are very small.
Parenchyma cells. 3. Parenchyma with starch. 4.
252 HISTOLOGY OF MEDICINAL PLANTS
In canella alba bark the periderm is composed of stone- cell cork or stone cells arranged in superimposed rows, which form the outer layers of the bark.
In white oak and most barks from woody trees the periderm consists of lifeless parenchyma, medullary rays, sieve cells, bast fibres, and in some cases stone cells and of phellogen cells.
In yoimg wild cherry, cascara sagrada, and frangula are several layers of tangentially elongated collenchyma cells with chlorophyll. In the older barks of the above and in many other barks no collenchyma cells occur.
In cramp bark and in tulip tree bark the outer layers of the cortical parenchyma cells are beaded. In most barks there is no beaded walled parenchyma. The outer layers of most cortical parenchyma cells are tangentially elongated while the inner parenchyma cells are mostly circular in outline.
In white oak, cascara sagrada and prickly ash are groups of stone cells; in the cinnamon barks are bands of stone cells; in cinchona bark are isolated stone cells. In cramp bark, mezerum, elm, and white pine bark no stone cells occur.
In frangula, cascara sagrada, codllina, cinnamon, cinchona, sassafras, and wild cherry barks the bast fibres occur in groups. In frangula, cascara sagrada, and cocillina the bast fibres are surrounded by crystal cells with crystals.
In sassafras bark mucilage cells occur. In canella alba, white pine, and sassafras barks secretion cells occur; but in most barks no secretion cells occur.
In sassafras bark the medullary ray cells are nearly as broad as long; in cramp bark they are elongated and oval in shape. In cascara sagrada, as in most barks, the cells are longer than broad and rectangular in shape.
In cascara sagrada the sieve cells are very large; in granatum bark the sieve cells are very small.
In cassia cinnamon and in canella alba bark the walls of the sieve cells have collapsed, with the result that the sieve cells have become partly obliterated.
In witch-hazel, mountain maple, willow, and black walnut are found prisms; in cramp bark, black haw, wahoo, pome- granate, and cotton root bark are found rosette crystals; in
BARKS 253
the cinnamon barks are found raphides; in cinchona bark, micro-crystals.
In cocillina, frangula, cascara sagrada, white oak, poplar and Jamaica dogwood barks are found crystal-bearing fibres (Plates 19 and 20).
When studying barks we must consider the kind, structure, and amount of the periderm; the nature of the phellogen; the nature and amount of the cortical parenchyma; the occurrence, distribution, and amount of stone cells, when present; the occurrence and structure of the bast fibres; the presence or absence of secretion cells; the width, distribution, and structure of the medullary rays.