517. The male and female moss plants.—The two plants of mnium shown in figs. [281], [282] are quite different, as one can easily see, and yet they belong to the same species. One is a female plant, while the other is a male plant. The sexual organs then in mnium, as in many others of the mosses, are borne on separate plants. The archegonia are borne at the end of the stem, and are protected by somewhat narrower leaves which closely overlap and are wrapped together. They are similar to the archegonia of the liverworts.
Fig. 281.
Female plant (gametophyte) of
a moss (mnium), showing
rhizoids below, and the
tuft of leaves above which
protect the archegonia.
Fig. 282.
Male plant (gametophyte) of
a moss (mnium) showing
rhizoids below and the
antheridia at the center
above surrounded by
the rosette of leaves.
The male plants of mnium are easily selected, since the leaves at the end of the stem form a broad rosette with the antheridia, and some sterile threads packed closely together in the center. The ends of the mass of antheridia can be seen with the naked eye, as shown in [fig. 282]. When the antheridia are ripe, if we make a section through a cluster, or if we merely tease out some from the end with a needle in a drop of water on the slide, then prepare for examination with the microscope, we can see the form of the antheridia. They are somewhat clavate or elliptical in outline, as seen in [fig. 284]. Between them there stand short threads composed of several cells containing chlorophyll grains. These are sterile threads (paraphyses).
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.
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.
