Epidermis. The epidermal cells are variable in shape and very large. There are no cell contents. Cortex. The cortex consists of collenchyma and parenchyma cells and stone cells. The collenchyma cells have very small, angled cavities and very thick walls. These cells make up the greater part of the cortex. The cortical parenchyma cells are variable in size and shape. The stone cells occur singly or in groups. The walls are thick, white, porous, and striated, and the central cavity is frequently quite large. Phloem. The phloem contains sieve cells, phloem parenchyma, and bast fibres. The sieve cells have thin, white, angled walls. The phloem parenchyma cells are frequently tangentially elongated, otherwise they resemble the sieve cells. The bast fibres occur alone or in groups. The walls are thick, white and porous.
<Callout type="important" title="Key Identification Features">Understanding the structure of horehound is crucial for identifying it correctly from its adulterants.</Callout> Cambium. The cambium cells are rectangular in shape and the walls are thin. Xylem* The xylem contains vessels, wood parenchyma, and medullary rays. The vessels are large; the walls are thick, white, and angled. The wood parenchyma cells are variable in size and shape and the walls are angled. The medullary ray cells are radially elongated and rectangular in shape. Pith Parenchyma. The pith parenchyma cells are large and rounded in shape.
POWDERED HOREHOUMD The structure of powdered horehound is shown in Chart 97. The epidermal cells of the leaf (i) are wavy in outline, the guard cells are elliptical, the stoma lens-shaped, the epidermis often showing hairy outgrowth as in the illustration. The epidermal cells of the petals (2) have irregularly thickened beaded walls. The non-glandular hairs from the calyx (3); the long, thin-walled, midticellular non-glandular twisted hairs (4) from the leaves and stems; long, thin-walled, unicellular hairs (5) from the tube of the corolla; the glandular hairs (6) with a one-celled stalk and with two secreting cells divided by vertical walls; the eight-celled glandular hair (7) as seen in surface and side view; the spiral and reticulated conducting cells (8); the thick, white-walled fibres from the stem (9); the pollen grains (10) with nearly smooth walls. The diagnostic elements of the U.S.P. horehound are the long, twisted, multicellular hairs (4), the glandular hairs (7), and the pollen grains (10).
POWDERED SPURIOUS HOREHOUND Marrubium perigrinum, which is a related species of horehound and which is a common adulterant of horehound, has the following structure: The wavy leaf epidermis (i) with stoma; the beaded wall petal epidermis (2); the non-glandular, multicellular branched hairs (3) from the stem leaves or flowers; the broken pieces and branches of the compound hairs (4) scattered throughout the field; the glandular hairs (5) with a two-celled stalk; the eight-celled glandular hair (7) seen in surface view and a side view (8) of a similar hair; the long, pointed, unicellular non-glandular hair from the tube of the corolla, the wall irregularly thickened near the apex; the fibres (9); the pollen grains (10) with prominent centrifugal projections; the conducting cells. The diagnostic elements of marrubium perigrinum are the multicellular branched hairs (3), which occur on all parts of the plant, usually much broken in the powder, with walls many times thicker than the hairs found in U.S.P. horehound; the pollen grains (10) with centrifugal projections and the stalked glandular hairs (5).
INSECT FLOWER STEMS Insect flower stems are the chief adulterant of insect flowers. Until the passage of the insecticide law, it was a common practice to sell (for insect powder) a mixture of powdered stems and flowers. Since the passage of the law, the presence of the stems in a powder is supposed to be declared on the label. The structure of powdered insect flower stems (Chart 99) is as follows: The epidermal cells of the stems are prominently marked with stoma and angled, striated wall cells. On cross-section the stem is seen to be made up of epidermal cells with thick outer and thin side walls. The T-shaped hairs are longer than those found on any other part of the plant. The fibres are the most characteristic part of the powder. They are elongated, and the walls are white and slightly porous and of nearly uniform thickness. They occur free in the field or in groups of two or more. The cross-section view of these fibres is shown in Fig. 5. The pith parenchyma is abundant and is composed of thick, porous-walled cells. On cross-section the cells are rounded and are separated by intercellular spaces. The conducting cells vary from spiral to reticulate.
Key Takeaways
- Understanding plant anatomy is crucial for identifying medicinal herbs accurately.
- Horehound and its adulterant, marrubium perigrinum, can be distinguished by their unique anatomical features.
- Insect flower stems are a common adulterant in insect powder products.
Practical Tips
- Use a microscope to examine plant powders for accurate identification of medicinal herbs.
- Learn the diagnostic elements of horehound and marrubium perigrinum to avoid misidentification.
- Be cautious when purchasing powdered herbal remedies, as adulteration is common.
Warnings & Risks
- Misidentifying plants can lead to ineffective or harmful treatments.
- Adulterants in medicinal powders may reduce efficacy and cause allergic reactions.
- Failure to declare adulterants on labels can result in legal penalties for manufacturers.
Modern Application
While the specific details of plant anatomy have advanced since 1916, understanding these foundational structures remains critical for herbalists and survivalists. Modern microscopy techniques enhance identification accuracy but the core principles remain unchanged.
Frequently Asked Questions
Q: What are the key differences between horehound and its adulterant marrubium perigrinum?
Horehound can be distinguished from marrubium perigrinum by its long, twisted multicellular hairs (4), eight-celled glandular hair (7), and smooth pollen grains (10). Marrubium perigrinum has thicker walls on its multicellular branched hairs and pollen grains with prominent centrifugal projections.
Q: How can one identify insect flower stems in powdered form?
Insect flower stems are identified by their elongated, white fibres with porous walls of nearly uniform thickness. These fibres often occur free or in groups and have a characteristic cross-section view shown in Fig. 5.
Q: Why is it important to identify adulterants like marrubium perigrinum?
Misidentification can lead to ineffective treatments, allergic reactions, and reduced efficacy of herbal remedies. Proper identification ensures the safety and effectiveness of medicinal plants used in treatment.