=518. Sporogonium.=—In fig. 280 we see illustrated a sporogonium of mnium, which is of course developed from the fertilized egg-cell of the archegonium. There is a nearly cylindrical capsule, bent downward, and supported on a long slender stalk. Upon the capsule is a peculiar cap,[29] shaped like a ladle or spatula. This is the remnant of the old archegonium, which, for a time surrounded and protected the young embryo of the sporogonium, just as takes place in the liverworts. In most of the mosses this old remnant of the archegonium is borne aloft on the capsule as a cap, while in the liverworts it is thrown to one side as the sporogonium elongates. [Illustration: Fig. 283. Section through end of stem of female plant of mnium, showing archegonia at the center. One archegonium shows the egg. On the sides are sections of the protecting leaves.] [Illustration: Fig. 284. Antheridium of mnium with jointed paraphysis at the left; spermatozoids at the right.] =519. Structure of the moss capsule.=—At the free end on the moss capsule as shown in the case of mnium in fig. 280, after the remnant of the archegonium falls away, there is seen a conical lid which fits closely over the end. When the capsule is ripe this lid easily falls away, and can be brushed off so that it is necessary to handle the plants with care if it is desired to preserve this for study. =520.= When the lid is brushed away as the capsule dries more we see that the end of the capsule covered by the lid appears “frazzled.” If we examine this end with the microscope we see that the tissue of the capsule here is torn with great regularity, so that there are two rows of narrow, sharp teeth which project outward in a ring around the opening. If we blow our “breath” upon these teeth they will be seen to move, and as the moisture disappears and reappears in the teeth, they close and open the mouth of the capsule, so sensitive are they to the changes in the humidity of the air. In this way all of the spores are prevented to some extent from escaping from the capsule at one time. =521.= Note. If we make a section longitudinal of the capsule of mnium, or some other moss, we find that the tissue which develops the spores is much more restricted than in the capsule of the liverworts which we have studied. The spore-bearing tissue is confined to a single layer which extends around the capsule some distance from the outside of the wall, so that a central cylinder is left of sterile tissue. This is the columella, and is present in nearly all the mosses. Each of the cells of the fertile layer divides into four spores. [Illustration: Fig. 285. Two different stages of young sporogonium of a moss, still within the archegonium and wedging their way into the tissue of the end of the stem. _h_, neck of archegonium; _f_, young sporogonium. This shows well the connection of the sporophyte with the gametophyte.]