. Botany; principles and problems. Botany. 338 BOTANY: PRINCIPLES AND PROBLEMS within the remains of the stout megaspore wall (Fig. 212). On the exposed tissue, a group of archegonia appear. Each microspore forms a single antheridium in which a group of biciliate sperms develops. The young sporophyte is thrust deeply into the tissues of the gametophyte until it has begun its differentiation. Such a life history as this is clearly a step in the direction of seed production. The genus Isoetes, the Quill wort (Fig. 213), is usually included among the lycopods although its remarkable characteristi
. Botany; principles and problems. Botany. 338 BOTANY: PRINCIPLES AND PROBLEMS within the remains of the stout megaspore wall (Fig. 212). On the exposed tissue, a group of archegonia appear. Each microspore forms a single antheridium in which a group of biciliate sperms develops. The young sporophyte is thrust deeply into the tissues of the gametophyte until it has begun its differentiation. Such a life history as this is clearly a step in the direction of seed production. The genus Isoetes, the Quill wort (Fig. 213), is usually included among the lycopods although its remarkable characteristics have. Fig. 212.—Female gametophyte of Selaginella. The stout wall of the micro- spore still encloses part of the gametophyte. At the right is an archegonium; at the center and left, young embryos which have arisen from fertilized eggs in other archegonia. The embryo is carried down into the tissue of the gameto- phyte by an elongated cell, the suspensor. In the larger embryo, the shoot (at right) and root (at left) are beginning to become differentiated, as well as the large, absorbing foot, at the lower left. (Mainly after Pfeffer). caused some botanists to place it in a distinct order. The plants grow in water or very moist places and each consists of a tuft of long, quill-like leaves, arising from a short and flattened stem. In the hollow bases of these leaves the sporangia are borne. Isoetes is heterosporous, its gametophytes being similar in general structure to those of Selaginella except that the sperms have many cilia. The lycopods were particularly prominent in the forests of the Coal Period, the great tree-like lepidodendrids and sigillarians belonging to this order. It is noteworthy that these ancient members of the group possessed a cambium and well developed secondary wood, tissues which are quite absent in living Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration a
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