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.