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.

In clover flowers the pollen grains are mostly rounded in outline, the wall is uniformly thickened, and cell contents are coarsely granular.

In belladonna flowers the pollen grains terminate in three blunt points.

In Spanish saffron the pollen grains are spherical and the cell contents are granular.

[Illustration: PLATE 113

SMOOTH-WALLED POLLEN GRAINS

1. Cloves (_Eugenia caryophyllata_, Thunb.). 2. Santonica (_Artemisia pauciflora_, Weber). 3. Elder (_Sambucus canadensis_, L.). 4. Century minor (_Erythræa centaurium_ [L.], Pers.). 5. Pichi (_Fabiana imbricata_, R. and P.). 6. Cyani. 7. Lavender (_Lavandula officinalis_, Chaix.). 8. Clover (_Trifolium pratense_, L.). 9. Belladonna (_Atropa belladonna_, L.). 10. Spanish saffron (_Crocus sativus_, L.).]

[Illustration: PLATE 114

SPINY WALLED POLLEN GRAINS

1. Anthemis (_Anthemis nobilis_, L.). 2. Arnica (_Arnica montana_, L.). 3. Calendula (_Calendula officinalis_, L.). 4. Cassia flowers. 5. American saffron (_Carthamus tinctorius_, L.). 6. Blue malva flowers (_Malva sylvestris_, L.).]

The non-spiny-walled pollen grains differ not only in microscopic appearance, but also in size. Clove pollen grains are the smallest, while Spanish saffron pollen grains are the largest.

NON-SPINY-WALLED POLLEN GRAINS

In cloves the pollen grains show a six-sided, angled cavity and an outer wall which terminates in three slightly pointed, narrowly notched portions, separated by nearly straight walls.

In santonica the pollen grains have smooth, unequally thickened walls, which are strongly constricted at three points, the outline resembling three half-circles placed together.

In elder flowers the pollen grains appear circular or three-parted. The wall is of nearly uniform thickness, even at the constricted part of the grain.

In century minor the pollen grains show three pronounced restrictions. The wall at these points is very thin. In pichi flowers the pollen grains are either circular or three-sided and three-pointed. Inside of each point there is a nearly white pore. In some of the grains the pollen tube has grown out of one of the pores.

In cyani flowers the pollen grains are longer than broad and the cell contents appear to be divided into two end portions and an elevated middle portion.

SPINY-WALLED POLLEN GRAINS

In anthemis the pollen grains have unequally thickened walls constricted in three places. The spines are short, broad at the base, and sharp-pointed.

In arnica flowers the pollen grains show three light-colored pores and numerous short spines.

In calendula flowers the pollen grains show one or more pores, typically three pores. These pores appear as white spots, and the wall immediately over the pore is smooth and thinner than the remaining part of the wall; the spines are very numerous.

In cassia flower pollen grains the outer wall is extended into a number of rounded projections which are frequently arranged in sets of fours.

In American saffron flowers the pollen grains show one, two, or three light-colored pores; the spines are short and broad.

In blue malva flowers the pollen grains are spherical and the outer wall extends into numerous spinelike projections.

It will be observed that the spiny-walled pollen grains differ greatly in size, the smallest being the pollen grain of anthemis and the largest being the pollen grain of blue malva flowers.

In matricaria are numerous, greenish-brown, spiny-walled pollen grains. In anthemis are multicellular, uniseriate non-glandular hairs with three or four short, broad, yellow-walled basal cells and a greatly elongated, thin, gray-walled apical cell.

In arnica are multiseriated branched hairs of the pappus, and numerous large, yellowish, spiny-walled pollen grains.

STIGMA PAPILLÆ

The =papillæ of the stigma= of most flowers form a characteristic element even when the flower is powdered. In the case of composite flowers the papillæ of the disk and ray flowers differ. In American saffron the papillæ of the style differ in a recognizable way from the papillæ of the stigma.

The papillæ of the stigma of the ray and disk flowers of arnica, anthemis, matricaria, and insect flowers differ greatly. Even the papillæ of the stigma of the ray and disk flowers differ. In all cases observed the papillæ of the ray flowers are smaller than the papillæ of the disk flowers.

The papillæ of the stigma of saffron (Plate 115, Fig. 3) are long and tubular. These papillæ are nearly uniform in diameter, and the apex is blunt and rounded. The wall is slightly granular in appearance. The papillæ of the stigma of American saffron (Plate 116, Fig. 2) are short and tubular. Each papilla is broadest at the base and tapers to a slender point. The papillæ of that part of the style which emerges from the corolla (Plate 116, Fig. 1) are large and curved, and the walls are very thick. The apex of the papilla is frequently solid.

The papillæ of the stigma of the ray flowers of anthemis (Plate 117, Fig. 1) have thin, slightly striated walls; while the papillæ of the stigma of the disk flowers (Plate 117, Fig. 2) are longer, the walls are thicker, and the cell content is denser.

[Illustration: PLATE 115

PAPILLÆ

1. Arnica ray flowers (_Arnica montana_, L.). 2. Insect flower disk (_Chrysanthemum cinerariifolium_ [Trev.], Vis.). 3. True saffron (_Crocus sativus_, L.).]

[Illustration: PLATE 116

PAPILLÆ OF STIGMAS

1. Stigma papillæ of American saffron (_Carthamus tinctorius_, L.) from that part of the style that emerges from the corolla. 2. Papillæ from the upper part of the stigma of American saffron. 3. Papillæ of the stigma of the disk flowers of arnica (_Arnica montana_, L.).]

[Illustration: PLATE 117

PAPILLÆ OF STIGMAS

1. Stigma papillæ of the ligulate flowers of anthemis (_Anthemis nobilis_, L.). 2. Stigma papillæ of the tubular flowers of anthemis. 3. Stigma papillæ of the ligulate flowers of matricaria (_Matricaria chamomilla_, L.). 4. Stigma papillæ of the disk flowers of matricaria. 5. Stigma papillæ of the ligulate flowers of insect flower (_Chrysanthemum cinerariifolium_ [Trev.], Vis.).]

The papillæ of the stigma of the ray (Plate 117, Fig. 3) and disk flowers (Plate 117, Fig. 5) of matricaria are similar in structure, but the papillæ of the disk flowers are larger.

The papillæ of the stigma of the ligulate flowers of insect flowers (Plate 117, Fig. 5) are tubular; the walls are striated, and in each papilla there is a small yellow globule, while the papillæ of the disk flowers (Plate 115, Fig. 2) are long and tubular, and the walls are thick.

The papillæ of the stigma of the ray flowers of arnica (Plate 115, Fig. 1) are very short and tubular. The walls are thin and the cell contents appear as small, bright-yellow globules, while the papillæ of the stigma of the disk flowers (Plate 116, Fig. 3) are broadest at the base, the apex is pointed, and the yellow globules are larger.

The =solitary= hairs are divided into the branched and non-branched hairs.

POWDERED INSECT FLOWERS

The microscopic examination of insect powder is difficult for the reason that there are so many elements to be constantly kept in mind. The parts of the flower which contribute characteristic cells are the stem, involucre, ray flowers, disk flowers, and the receptacle. In each of these parts there are many different types of cells.

There are practically two types of flowers found in insect powder of commerce: first, closed or immature flowers, and secondly, open or mature flowers. As explained above, the half-open flowers consist largely of the two above-named varieties. Let us first consider the structure of the closed insect flowers as illustrated in Plate 118.

[Illustration: PLATE 118

POWDERED CLOSED INSECT FLOWER (_Chrysanthemum cinerariifolium_, [Trev.] Vis.)

1. Edge of scale. 2. Fibre of scale. 3. Hairs. 4. Upper epidermis of ray flower. 5. Under epidermis of ray flower. 6. Cross-section of ray petal. 7. Parenchyma of ray flowers with crystals. 8. Lobe of disk petal. 9. Filament tissue. 10. Calyx tissue, 11. Lobe of stamen. 12. Pollen. 13. Papillæ of stigma. 14. Secretion cavity with surrounding cells. 15. Parenchyma of the receptacle.]

The involucre has many characteristic cells. The more prominent ones seen in the powder are the edge of the scale with the attached hair (Fig. 1). These hairs (Fig. 3) are T-shaped. The terminal cell is expanded laterally, and it terminates in two points. Connecting the terminal cell with the epidermis are two or three cells which are slightly longer than broad. In the powder the terminal cell is usually attached to fragments only of the supporting cells. Fibres of the bracts have thick, wavy, porous walls, and they have a tendency to occur in masses. The upper epidermis (Fig. 4) of the ray-flower petal is prominently papillate. The under epidermis consists of wavy cells without papillæ. Another view of the papillæ is shown in Fig. 6. The parenchyma of the ray flowers (Fig. 7) contain cubical crystals. The lobe of the disk-flower petal (Fig. 8) is papillate at the end, the terminal cells have thick outer and thin inner walls. The filament tissue (Fig. 9) is composed of nearly square cells. The calyx tissue (Fig. 10) is made up of thin-walled cells with slightly papillate margins. The lobe of the stamen (Fig. 11) consists of nearly uniform epidermal cells which are in contact throughout their long diameter, while the hypodermal cells are thin-walled and angled. The pollen grains (Fig. 12) are dark yellowish green, thin, and the wall does not appear perforated by pores. The papillæ of the stigma (Fig. 13) are clustered, club-shaped, and nearly white in color. They are usually found detached in the powder. All parts of the pistil contain secreting cells, but the most conspicuous secreting cavities (Fig. 14) are those of the ovary. These cavities appear brownish in color and are surrounded by small cells which appear indistinct on account of the great number of superimposed cells. The parenchyma of the receptacle occurs in fragments which have strongly marked porous walls.

OPEN INSECT FLOWERS

Many of the structures of open insect flowers (Plate 119) are similar to those found in the closed flower. There is practically no difference in the edge of the scale (Fig. 1); or the fibre of the scale (Fig. 2); or the T-shaped hairs (Fig. 3); or the upper epidermis of the ray flower (Fig. 4); or the under epidermis of the ray flower (Fig. 5); or the cross-section of the ray petal (Fig. 6); or the lobe of the disk petal (Fig. 7); or the filament tissue (Fig. 8); or the lobe of the stamen (Fig. 9); or the papillæ of the stigma (Fig. 12); or the parenchyma of the receptacle (Fig. 15). The difference in structure is found, first, in the involucre scales, which are more fibrous than the scales of the closed flowers; secondly, in the pollen (Fig. 11), which is less abundant than in the closed flower; it is also lighter in color and usually shows the wall perforated by three pores; thirdly, the outer layers of the achene consist of thick, porous-walled stone cells (Fig. 13), which occur singly or in groups; fourthly, the secretion cavity is broader and darker in color (Fig. 14). These differences enable one at once to distinguish between the closed and open insect flowers. Now, since the half-closed flowers consist almost wholly of a mixture of equal parts of closed and open flowers, it follows that the elements of these two flowers will be mixed in about equal proportions. Thus we are able to distinguish microscopically the three commercial varieties of insect powder--namely, closed insect flowers, open insect flowers, and half-open insect flowers.

[Illustration: PLATE 119

POWDERED OPEN INSECT FLOWER (_Chrysanthemum cinerariifolium_, [Trev.] Vis.)

1. Edge of involucre scale. 2. Fibres of involucre scale. 3. Hairs. 4. Upper epidermis of ray flower. 5. Under epidermis of ray flower. 6. Cross-section of ray petal. 7. Lobe of disk flower. 8. Filament tissue. 9. Lobe of stamen. 10. Calyx tissue, 11. Pollen. 12. Papillæ of the stigma. 13. Stone cells from the achene and cross-section of achene. 14. Secretion cavity with surrounding cells. 15. Parenchyma of the receptacle.]

Insect flowers are the most valuable vegetable insecticide known; yet much of its effectiveness is destroyed by the adulterants which are so readily identified by the compound microscope.

POWDERED WHITE DAISIES

A common adulterant found in open insect flowers is the flower-heads of European daisy (_C. leucanthemum_). Examination of powdered flowers exported from Europe shows that the entire flower-head is ground and mixed with the insect flowers. In the cheaper varieties of open flowers, only the tubular flowers are added after they have been separated from the heads by crushing and sifting. These tubular flowers so closely resemble the tubular flowers of the true insect flowers that it is practically impossible to distinguish between them macroscopically. The quickest and surest way to identify them is to reduce a portion of the flowers to a fine powder and examine it microscopically.

Certain structures of the white daisies (Plate 120) are somewhat similar to those found in insect flowers. These structures are the papillæ of the ray petal (Figs. 3, 5, and 13), the lobe of the disk petal (Fig. 14), and the lobe of the stamen and the pollen (Fig. 8).

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.

[Illustration: 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.

##