Fig. 241.—Cycas: a stamen (nat. size) seen from the under side; b four pollen-sacs, not yet open, forming a “sorus”; c three open pollen-sacs; d a pollen-grain.
Fig. 242.—Stamens of Araucaria (pollen-sacs long and pendulous).
Fig. 243.—Male flower of Taxus.
Fig. 244.—A Cross section through a quadrilocular anther in different stages of development: s the seam where it bursts open; vf vascular bundle; k connective. B A stamen. C Another stamen seen from the front (f) and from the back (b).
Stamens. In the lowest Phanerogams (Cycadeæ) there are many indications of relationship to the Ferns. The stamens are flat and broad, and have on the back many pollen-sacs (microsporangia) arranged in small groups (true sori), which even have a small “placenta,” similar to the one possessed by the Ferns, and open towards the inside by a longitudinal cleft (Fig. [241], compare Fig. [213]). A section of the Coniferæ agree more closely with the Equisetaceæ, in having a few (three to eight) pollen-sacs arranged on the underside of more or less shield-like leaves (Figs. [242], [243], compare with Fig. [224] a, c, d). In the Abietaceæ the number of sporangia is diminished to two, which are placed also on the lower side (Fig. [267]) of a stamen. The number of pollen-sacs (microsporangia) in the Angiosperms is nearly always four to each stamen; they are longitudinal projections which are placed in pairs on each side of the central line of the stamen, two on the edge, and the other two generally on the side which is turned inwards; the pollen-sacs generally dehisce longitudinally (quadrilocular anthers, Fig. [244]). A few, for instance Orchidaceæ and Asclepiadaceæ, have only two pollen-sacs (bilocular anthers); and in others, such as Solanum and the Ericaceæ, they open by pores; in Lauraceæ and Berberidaceæ, by valves. The part of the stamen which bears the pollen-sacs is termed the anther. Most frequently this is supported by a stalk known as the filament.
