=511. Order Jungermanniales.=[27]—There are two subdivisions of this order. _The Anacrogynæ_ include chiefly thalloid forms with continued apical growth, the archegonia back of the apical cell. Examples: Blasia, Aneura, Pellia, etc. _The Acrogynæ_ include chiefly foliose forms, the archegonia arising from the apical cell and in such cases interrupting apical growth. Examples: Cephalozia, Frullania, Bazzania, Jungermannia, Ptilidium, Porella, etc. CLASS ANTHOCEROTES. =512. The Anthocerotes= have formerly been placed with the Hepaticæ as an order. But because of their wide divergence from the other liverworts in the development of the sexual organs, and especially in the structure of the sporophyte, they are now by some separated as a distinct class. There is one order. =Order Anthocerotales.=[28]—This includes one family (Anthocerotaceæ) with Anthoceros and Notothylas in Europe and North America, and Dendroceros in the tropics. The latter is epiphytic. FOOTNOTES: [25] May be used as an alternate study for marchantia. [26] As subclass in Engler and Prantl. [27] As subclass in Engler and Prantl. [28] As subclass in Engler and Prantl. CHAPTER XXV. MOSSES (MUSCI). =513.= We are now ready to take up the more careful study of the moss plant. There are a great many kinds of mosses, and they differ greatly from each other in the finer details of structure. Yet there are certain general resemblances which make it convenient to take for study almost any one of the common species in a neighborhood, which forms abundant fruit. Some, however, are more suited to a first study than others. (Polytrichum and funaria are good mosses to study.) =514. Mnium.=—We will select here the plant shown in fig. 280. This is known as a mnium (M. affine), and one or another of the species of mnium can be obtained without much difficulty. The mosses, as we have already learned, possess an axis (stem) and leaf-like expansions, so that they are leafy-stemmed plants also. Certain of the branches of the mnium stand upright, or nearly so, and the leaves are all of the same size at any given point on the stem, as seen in the figure. There are three rows of these leaves, and this is true of most of the mosses. =515.= The mnium plants usually form quite extensive and pretty mats of green in shady moist woods or ravines. Here and there among the erect stems are prostrate ones, with two rows of prominent leaves so arranged that it reminds one of some of the leafy-stemmed liverworts. If we examine some of the leaves of the mnium we see that the greater part of the leaf consists of a single layer of green cells, just as is the case in the leafy-stemmed liverworts. But along the middle line is a thicker layer, so that it forms a distinct midrib. This is characteristic of the leaves of mosses, and is one way in which they are separated from the leafy-stemmed liverworts, the latter never having a midrib. [Illustration: Fig. 280.