By making a series of longitudinal sections with a sharp razor through the top of the plant, and magnifying sufficiently, it is found to end in a single, nearly hemispherical cell (Fig. 23, _B_, _S_). This from its position is called the "apical cell," and from it are derived all the tissues of the plant. Segments are cut off from its base, and these divide again into two by a wall parallel to the first. Of the two cells thus formed one undergoes no further division and forms the central cell of an internode (_y_); the other divides repeatedly, forming a node or joint (_x_). As the arrangement of these cells is essentially the same in the leaves and stem, we will examine it in the former, as by cutting several cross-sections of the whole bunch of young leaves near the top of the plant, we shall pretty certainly get some sections through a joint. The arrangement is shown in Figure 23, _E_. As the stem grows, a covering is formed over the large internodal cell (_y_) by the growth of cells from the nodes. These grow both from above and below, meeting in the middle of the internode and completely hiding the long axial cell. A section across the internode shows the large axial cell (_y_) surrounded by the regularly arranged cells of the covering or cortex (Fig. 23, _D_). All the cells contain a layer of protoplasm next the wall with numerous oval chloroplasts. If the cells are uninjured, they often show a very marked movement of the protoplasm. These movements are best seen, however, in forms like _Nitella_, where the long internodal cells are not covered with a cortex. In _Chara_ they are most evident in the root hairs that fasten the plant to the ground. The growth of the leaves is almost identical with that of the stem, but the apical growth is limited, and the apical cell becomes finally very long and pointed (Fig. 23, _C_). In some species the chloroplasts are reddish in the young cells, assuming their green color as the cells approach maturity. The plant multiplies non-sexually by means of special branches that may become detached, but there are no non-sexual spores formed. The sexual organs have already been noticed arising in pairs at the joints of the leaves. The oögonium is formed above, the antheridium below.