But among certain of the highest _Algæ_, we _do_ find something more than this union of the pseud-axial with the pseudo-foliar structure. In addition to pseud-axes of comparative complexity; and in addition to pseudo-folia that are like leaves, not only in their general shapes but in having mid-ribs and even veins; there are the beginnings of a higher stage of integration. Figs. 38, 39, and 40, show some of the steps. In _Rhodymenia palmata_, Fig. 38, the parent-frond is comparatively irregular in form, and without a mid-rib; and along with this very imperfect integration, we see that the secondary fronds growing from the edges are distributed very much at random, and are by no means specific in their shapes. A considerable advance is displayed by _Phyllophora rubens_, Fig. 39. Here the frond, primary, secondary, or tertiary, betrays some approach towards regularity in both form and size; by which, as also by its partially-developed mid-rib, there is established a more marked individuality; and at the same time, the growth of the secondary fronds no longer occurs anywhere on the edge, in the same plane as the parent-frond, but from the surface at specific places. _Delesseria sanguinea_, Fig. 40, illustrates a much more definite arrangement of the same kind. The fronds of this plant, quite regularly shaped, have their parts decidedly subordinated to the whole; and from their mid-ribs grow other fronds which are just like them. Each of these fronds is an organized group of those morphological units which we distinguish as aggregates of the first order. And in this case, two or more such aggregates of the second order, well individuated by their forms and structures, are united together; and the plant composed of them is thus rendered, in so far, an aggregate of the third order. Just noting that in certain of the most developed _Algæ_, as the _Sargassum_, or common gulf-weed, this tertiary degree of composition is far more completely displayed, so as to produce among Thallophytes a type of structure closely simulating that of the higher plants, let us now pass to the consideration of these higher plants.