158. (Figs. 155 and 156.) PRUNUS SEROTINA. Wild

cherry Bark. U. S.

Fl. ex. 20. Inf. 40.

Wildekirschenrinde, G. Ecorce de cérisier, Fr.

The bark of Prunus serotina Ehrhart, Rosaceæ.
Bright reddish brown.

Somewhat aromatic, recalling bitter almonds.
Bitter and astringent.

Numerous typical thickwalled, porous sclerenchyma cells. Bast fibers comparatively few; some branching, irregular, sclerenchymatous. Aggregate and prismatic crystals of calcium oxalate abundant in bark parenchyma cells. (Fig. 156.)

Ash 4 per cent.

The bark of choke cherry (Prunus virginiana Miller) (Fig. 155) differs from the above in the absence of sclerenchyma cells; bast fibers normal and branching, are very abundant; aggregate crystals very numerous and some quite large; prismatic crystals are wanting; middle bark parenchyma cells small and loosely united.

Fig. 155. PRUNUS VIRGINIANA. (Choke Cherry.).

a. Bast, simple and branching.

b. Parenchyma cells.

c. Aggregate crystals.

159. PULSATILLA. Pulsatilla.

Fl. ex. 30.

Pasque flower, E. Küchenschelle, G. Pulsatille, Coquelourde, Fr. The flowering herb of Anemone pratensis L. Ranunculaceæ.

Greenish.

Fragrant; hay odor.

Somewhat pungent.

Vertical wall of lower epidermal cells wavy, of upper epidermis only slightly so. Stomata above and below. Some of the leaf parenchyma cells filled with cryptocrystalline calcium oxalate. Long (500 microns) single celled, thick-walled, simple trichomes and some single celled. Indian club-shaped, thin-walled glandular trichomes. Some sclerenchymatous cells.

160. (Fig. 157). PYRETHRUM INSECT POWDER. Insect

Powder.

The partially expanded flower heads of Pyrethrum species. Compositæ.

Fine powder. Non-characteristic feel.

Yellowish brown.

Somewhat aromatic.

Somewhat pungent.

P. roseum, P. Marshallii and P. cinerariaefolium are the official species as named by the U. S. Insecticide Board. The histology of the three species is closely similar. Vascular tissue, parenchymatous tissue, T-shaped trichomes (basal cells usually broken and removed, leaving the tapering pointed end cell plainly to be seen). The pollen grains (spherical with incompletely developed conical projections on exine) should be abundantly present, though mostly immature. Some typical sclerenchyma cells (from torus); also aggregate crystals. A good quality of insect powder should show on an average at least 15 immature pollen grains in the field of the compound microscope (high power-No. 2 oc. and No. 7 obj.).

Ash 6 to 7 per cent. Impurities (inclusive of pyrethrum stems) should not exceed 15 per cent.

Very commonly adulterated. Most common adulterants are pyrethrum stems (excess of fibrous tissue and pollen grains few or none) also suspect old flower heads (few mature pollen grains, abundant seed tissue, sclerenchyma cells excessive); flower heads of related species, of calendula, of chamomile, etc.; sawdust, curcuma, mustard hulls, flour, corn meal, etc. A standard based upon the number of pollen grains present should be adopted. An insect powder showing less. than an average of 3 to 5 immature pollen grains to the field (high power) of the compound miscroscope should be rejected.

a. Epidermal cells.

Fig. 157. PYRETHRUM. Flowers.

b. Epidermis, lateral view.

c. Trichomes.

d. Sclerenchyma.

e. Pollen grains.

f. Parenchyma with crystals.

g. Tracheids.

161. (Fig. 158.) PYRETHRUM. Pellitory. U. S.

Tinct. 40.

Roman pellitory, E. Römische Bertramwurzel, G. Pyrèthre, Salivaire, Fr.

The roots of Anacyclus Pyrethrum D. C., Compositæ.
Pale brown.

Aromatic; recalling taraxacum.

Extremely and persistently pungent.

Some brown cork tissue. Rather large parenchyma cells, most of which contain inulin. Typical and somewhat elongated sclerenchyma cells. Lumps of yellow resin from the resin bearing ducts. Reticulate and some spiral ducts of medium diameter. Inner parenchyma cells elongated. No starch.

Ash 5 per cent.

Not generally adulterated. Taraxacum roots may be added.