=492. Development of the sporogonium.=—It will be interesting to note briefly how the development of the marchantia sporogonium differs from that of riccia. The first division of the fertilized egg is the same as in riccia, that is a wall which runs crosswise of the axis of the archegonium divides it into two cells. In marchantia the cell at the base develops the stalk, so that here there is a radical difference. The outer cell forms the capsule. But here after the wall is formed the inner tissue does not all go to make spores, as is the case with riccia. But some of it forms the elaters. While in riccia only the outside layer of cells of the sporogonium remained sterile, in marchantia the basal half of the egg remains completely sterile and develops the stalk, and in the outer half the part which is formed from some of the inner tissue is also sterile. [Illustration: Fig. 267. Section of developing sporogonia of marchantia; _nt_, nutritive tissue of gametophyte; _st_, sterile tissue of sporophyte; _sp_, fertile part of sporophyte; _va_, enlarged venter of archegonium.] =493. Embryo.=—In the development of the embryo we can see all the way through this division line between the basal half, which is completely sterile, and the outer half, which is the fertile part. In fig. 267 we see a young embryo, and it is nearly circular in section although it is composed of numerous cells. The basal half is attached to the base of the inner surface of the archegonium, and at this time the archegonium still surrounds it. The archegonium continues to grow then as the embryo grows, and we can see the remains of the shrivelled neck. The portion of the embryo attached to the base of the archegonium is the sterile part and is called the “foot,” and later develops the stalk. The sporogonium during all the stages of its development derives its nourishment from the gametophyte at this point of attachment at the base of the archegonium. Soon, as shown in fig. 267 at the right, the outer portion of the sporogonium begins to differentiate into the cells which form the elaters and those which form spores. These lie in radiating lines side by side, and form what is termed the _archesporium_. Each fertile cell forms four spores just as in riccia. They are thus called the mother cells of the spores, or spore mother cells. =494. How marchantia multiplies.=—New plants of marchantia are formed by the germination of the spores, and growth of the same to the thallus. The plants may also be multiplied by parts of the old ones breaking away by the action of strong currents of water, and when they lodge in suitable places grow into well-formed plants. As the thallus lives from year to year and continues to grow and branch the older portions die off, and thus separate plants may be formed from a former single one. [Illustration: Fig. 268. Marchantia plant with cupules and gemmæ; rhizoids below.]