=The sporangia-bearing leaves--Sporophylls.= In the Mosses the asexual generation is only represented by the sporogonium, and if the theory is correct which considers the sporogonium to be an embryo consisting of a rudimentary stem and terminal leaf, then the spores are produced on the leaves in these plants. The sporangia in the Filicinæ are situated in groups (sori) on the back or on the edge of the leaves. The number of sporangia in the sorus diminishes very greatly in the Marattiaceæ and Gleicheniaceæ (three to four in the latter, Fig. 213). In the Equisetinæ the sporangia are situated in a small number on the underside of shield-like leaves, and in Lycopodinæ, singly, in the axils of the fertile leaves, which are alike and bear either micro- or macrosporangia. In the Phanerogams there is a great difference between the stamens and carpels. [Illustration: 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.] [Illustration: FIG. 242.--Stamens of _Araucaria_ (pollen-sacs long and pendulous).] [Illustration: FIG. 243.--Male flower of _Taxus_.] [Illustration: 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_.