In the companion female receptacles at an early age, certain objects called archegonia (fig. 45) are found to be concealed between membranes which connect the spokes of the whorl at their origin. These archegonia are shaped like flasks with long necks, and each has a germ cell in its interior, into which a canal leads down from the extremity of the neck. When this embryo or germ cell is fertilized by the spermatozoids, instead of producing a new plant resembling its parent, the embryo cell developes itself into a sporangium containing spores, which are isolated cells enclosed in firm yellow envelopes and elaters, or ovoidal cells, each containing a double spiral fibre coiled up in its interior. This fibre is so elastic, that when the surrounding pressure is withdrawn by the bursting of the sporangium at maturity, the spires suddenly extend themselves with such force as to tear open the cell membrane, and jerk forth the spores which may be adhering to their coils, and thus to assist in their dispersion. The spores, when they germinate, develope themselves into little collections of cells, which gradually assume the form of a flattened frond.[66] It is only when exposed to light and air that the Marchantias have regular fructification; in shady places they are reproduced by buds placed in open conceptacles, which are formed out of green globules that appear in different parts of the frond, and after a time split open at the summit and expand into singularly graceful cups or baskets, whose edges are sharply and regularly indented so as to form a glistening fringe of teeth, while each tooth is adorned with a narrow fringe. When mature, the basket contains a number of little green round or oval discs raised on footstalks, and composed of two or more rows of cells. As soon as these objects, called gonidia, are ripe, they are detached from their stalks, and being washed out of their basket by the rain, they quickly grow on the moist earth around; sometimes they germinate before they leave their nest, and form irregular lobes on the parent plant. The Marchantia polymorpha, so admirably constructed, occurs in all temperate climates, and can bear considerable heat provided it has abundant moisture. The Marchantiaceæ are divided into three groups, containing fifteen genera, which are distinguished from each other by the character of their fructification. They are minutely described in Mr. Berkeley’s ‘Cryptogamic Botany;’ and are widely dispersed both in temperate and tropical countries, most of the genera being represented in Europe.