| |elaters. | | ----------------+--------------+------------+--------------+--------- Mosses |Fertilized |Sterile part|Cylindrical | { Mnium, |egg. (Develops|of stalked |layer of | { Funaria, |sporogonium.) |capsule is |cells around | { Polytrichum,| |stalk, wall |columella is | { etc. | |of capsule |the | Spores. | |of several |archesporium; | | |layers, |it | | |columella, |develops .....| | |lid, teeth | | | |etc., of | | | |the highly | | | |specialized | | | |capsule. | | ---------------+--------------+------------+--------------+--------- FOOTNOTES: [29] Called the calyptra. [30] As subclass in Engler and Prantl. [31] As subclass in Engler and Prantl. [32] As subclass in Engler and Prantl. [33] As subclass in Engler and Prantl. CHAPTER XXVI. FERNS. =529.= In taking up the study of the ferns we find plants which are very beautiful objects of nature and thus have always attracted the interest of those who love the beauties of nature. But they are also very interesting to the student, because of certain remarkable peculiarities of the structure of the fruit bodies, and especially because of the intermediate position which they occupy within the plant kingdom, representing in the two phases of their development the primitive type of plant life on the one hand, and on the other the modern type. We will begin our study of the ferns by taking that form which is the more prominent, the fern plant itself. =530. The Christmas fern.=—One of the ferns which is very common in the Northern States, and occurs in rocky banks and woods, is the well-known Christmas fern (Aspidium acrostichoides) shown in fig. 286. The leaves are the most prominent part of the plant, as is the case with most if not all our native ferns. The stem is very short and for the most part under the surface of the ground, while the leaves arise very close together, and thus form a rosette as they rise and gracefully bend outward. The leaf is elongate and reminds one somewhat of a plume with the pinnæ extending in two rows on opposite sides of the midrib. These pinnæ alternate with one another, and at the base of each pinna is a little spur which projects upward from the upper edge. Such a leaf is said to be pinnate. While all the leaves have the same general outline, we notice that certain ones, especially those toward the center of the rosette, are much narrower from the middle portion toward the end. This is because of the shorter pinnæ here.