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.
POWDERED INSECT FLOWER LEAVES (_Chrysanthemum cinerariifolium_ [Trev.], Vis.)
1. Upper epidermis. 2. Under epidermis showing stoma and hair scar. 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 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.