The differences are as follows: The under epidermis of the ray flowers is composed of wavy cells which are more elongated than the ray flowers of the under epidermis of the ray petal of insect flower. The filament tissue is made up of slightly beaded cells instead of smooth-walled cells. The papillæ of the stigma are smaller than the papillæ of insect flowers. The most striking difference is found in the structure of the achene. The epidermal tissue of the achene is composed of palisade cells (Fig. 10), which in the mature form have thick white walls and scarcely any cavity. These cells swell perceptibly when placed in water. The other striking feature of the achene is the bright red resin masses which occur free in the field. Even a small trace of daisies in insect powder can be identified.
PLATE 120
Powdered White Daisies (Chrysanthemum leucanthemum, L.)
1 and 2. Scale tissue. 3, 5 and 13. Papillæ of petals. 4. Scale tissue. 6. Lobe of ray petal. 7. Filament tissue. 8. Pollen. 9. Papillæ of stigma. 10. Palisade cells of achene. 11. Resin masses. 12. Parenchyma of receptacle. 14. Lobe of dish petal.
When studying flowers there should be considered the number and structure of pollen grains; the nature of the papillæ of the stigma and the petals; the nature of the hairs of the corolla and calyx, when present. In the composite flowers we should also consider the structure of the involucre scales, and, when present, the structure of the receptacle scales, as in the case of anthemus, and of the pappus hairs, as in the flowers of arnica, boneset, grindelia, and aromatic goldenrod.
CHAPTER VIII
FRUITS
There is great variation in the structure of fruits, such a variation, in fact, that no one fruit has a structure typical of all the other fruits. Each fruit, however, has a pericarp and one or more seeds. The amount and structure of the cells forming the pericarp and the seeds of fruits differ in different fruits, but for each fruit there is a normal amount of, and a characteristic, cellular structure. Nearly all the important medicinal fruits are cremocarps or umbelliferous fruits.
The plan of structure of cremocarps is similar, but they all have a different cellular structure. The epidermis may be simple or modified as papillæ or hairs. The secretion cavities may be absent (conium), or, when present, variable in number—cultivated celery seed has six, wild celery seed up to twelve, and anise up to twenty. The vascular bundles may be large or small. The endocarp cells may be two or more layers in thickness. The spermoderm may be thin or thick.
The endosperm cells may vary in size and the cell contents may vary.