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.
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.
CHAPTER VII
FLOWERS
The histological structure of flowers is readily seen in the powder; therefore, in studying flowers, it is not necessary to section the various parts. Each part of the flower should be isolated and powdered separately and each separated part studied. In each case the powders will contain surface, cross-, and radial sections of the parts powdered. While studying flowers, special attention should be given to the pollen grains, to the papillæ of the petals, to the papillæ of the stigma, and, in certain flowers, to the style tissue. In the composite flowers special attention should also be given to the involucre scales, to the scales of receptacle, and, when present, to the pappus. In addition, attention must be given to secretion cavities, as in cloves.
POLLEN GRAINS
Pollen grains are one of the most characteristic elements found in powdered flowers, because they are so small that they are not broken up when the drug is milled.
The two principal groups of pollen grains are, first, those with non-spiny walls (Plate 113); and, secondly, those with spiny walls (Plate 114), as shown in the two charts.
In lavender flowers the pollen grains have six constrictions of the outer wall. This wall is slightly striated and the cell contents are granular.