| The young sporogonium is protected by a thick calyptra derived from the tissue of the thallus around the archegonium. |
| Although more than one archegonium may be fertilized, only one gives rise to a viable embryo. |
| The axis of the embryo is inclined to that of the archegonium and may be almost at right angles. |
| In the club mosses the zygote divides in a plane at right angles to the axis of the archegonium. |
| An archegonium consists of neck cells and a large egg cell. |
| The archegonium has the form of a narrow flask with a long neck. |
