Under Epidermis

The under epidermal cells are uniformly smaller than the upper epidermal cells.

It is thus seen that mountain laurel leaf has no hypodermal cells; no spongy parenchyma; no under palisade cells; no under hypodermal cells, and no secretion cavities.

Plate 110. Cross-Section Mountain Laurel (Kalmia latifolia, L.).

1. Hair. 2. Epidermis. 3. Palisade parenchyma. 4. Parenchyma. 5. Under epidermis. 6. Intercellular space. 7. Rosette crystal. 8. Chlorophyll.

Trailing Arbutus

Epidermis

The epidermal cells of the trailing arbutus (Plate 111, Fig. 2) are variable in size. Many of the cells are modified, as guard cells (Fig. 1).

Parenchyma

The parenchyma cells are round and they are compactly arranged (Fig. 3) on the upper side of the leaf, but on the under side they are arranged in round, small, intercellular spaces (Fig. 5). In some of the intercellular spaces are rosette crystals (Fig. 7).

Under Epidermis

The under epidermal cells are smaller than the upper epidermal cells.

It will be seen that the structure of trailing arbutus leaf is very simple and that its structure is different from that of klip buchu and mountain laurel.

The structure of powdered leaves is very variable, yet characteristic for a given species. The leaves from the insect flower plant are collected with the stems, and ground and sold as a substitute for insect flowers. These leaves, when powdered, show the following structure (Plate 112):

Plate 111. Cross-Section Trailing Arbutus Leaf (Epigaea repens, L.).

1. Stomata. 2. Epidermis. 3. Parenchyma. 4. Cell with chlorophyll. 5. Intercellular space. 6. Under epidermis. 7. Rosette crystal.

Both the upper and lower epidermis have stomata (Figs. 1 and 2), but they differ in that the surrounding cells of the upper epidermis are wavy, while the corresponding cells of the under epidermis are similar, though the under epidermis has many attached hairs (Figs. 3 and 4). The T-shaped hairs form the most abundant element of the powder. They are similar in structure to those found on the scales and stem. Fragments of the mesophyll have round cells and contain chlorophyll (Fig. 6). The conducting cells are spiral or reticulate.

The different cells of the leaf differ greatly in structure, in amount, and in arrangement. In uva-ursi, boldus, pilocarpus, eucalyptus, and chimaphila leaves the outer walls of the epidermal cell is very thick. In uva-ursi leaves this thick wall appears bluish green when viewed under low power of the microscope.

In belladonna, stramonium, henbane, peppermint, spearmint, digitalis, and horehound, the outer wall of the epidermal cells is thin.

In witch-hazel, stramonium, coca, phytolacca, and peppermint there is a single layer of palisade parenchyma on the upper surface only of the leaf.

In senna there is one layer of palisade parenchyma on the upper and one layer on the under side of the leaf. In matico and tea leaves there are two layers of spongy parenchyma on the upper side of the leaf.

In chestnut leaves there are three layers of palisade parenchyma on the upper side of the leaf.

In eucalyptus leaves the entire central part of the leaf, with the exception of the secretion cells and fibro-vascular bundle, is made up of the palisade parenchyma.

In some leaves no palisade parenchyma occurs. Trailing arbutus (Plate 111) is an example of such a leaf.

In stramonium leaves the spongy parenchyma is strongly branched; in mountain laurel the spongy parenchyma is mostly non-branched and circular in form, as in trailing arbutus (Plate 111, Fig. 3), and as occurs in the midrib portion of most leaves.

In stramonium and chestnut are found rosette crystals. In henbane, coca, and senna are found prisms. In belladonna, scapola, and tobacco leaves are found micro-crystals. In most leaves no crystals occur. In witch-hazel and tea leaves stone cells occur, but in most leaves there are no stone cells. In eucalyptus, thyme, jaborandi, buchu, rosemary, and white pine leaves are secretion cells; while in belladonna, stramonium cells occur. In senna and coca leaves are crystal-bearing fibres; most leaves do not have crystal-bearing fibres.

Plate 112. Powdered Insect Flower Leaves.{Chrysanthemum cinerariifolium [Trev.], Vis.)

1. Upper epidermis. 2. Under epidermis showing stoma and hair sear. 3. Cross-section of under epidermis with attached hair. 4. Cross-section of upper epidermis. 5. Hairs. 6. Mesophyll with chlorophyll bodies. 7. Conducting cells.

In chimaphila and uva-ursi there are no outgrowths from the epidermal cells.

In senna, witch-hazel, chestnut, and coca, numerous non-glandular hairs occur on the epidermis. In tobacco, belladonna, henbane, pennyroyal, peppermint, and spearmint both glandular and non-glandular hairs occur on the epidermis..

When studying leaves there should be considered the absence or presence of outgrowths and their nature; the nature of the epidermis and, when present, the number of layers of the hypodermis; the nature of the stoma, whether raised above, even with, or below the level of the epidermis; the number of layers, and the distribution, when present, of the palisade parenchyma; the form and amount of the spongy parenchyma; the absence or presence of secretion cells; the nature and form of the fibro-vascular bundles, and the nature and amount of the organic and inorganic cell contents.