. Morphology of gymnosperms. Gymnosperms; Plant morphology. CYCADOFILICALES 33 each chamber being traversed longitudinally by a single vascular strand, the strands being connected with the main bundle that enters the chalaza. The pollen chamber is peculiar in that it is not the usual open cavity in the beak of the nucellus, but is a cylindrical (bell- shaped) crevice between the epidermis of the free tip of the nucellus and its central core of tissue (fig. 27). The archegonia probably occurred in a ring be- neath this crevice, preparations. Our of L. ovoides from Lomax show the method of forma

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. Morphology of gymnosperms. Gymnosperms; Plant morphology. CYCADOFILICALES 33 each chamber being traversed longitudinally by a single vascular strand, the strands being connected with the main bundle that enters the chalaza. The pollen chamber is peculiar in that it is not the usual open cavity in the beak of the nucellus, but is a cylindrical (bell- shaped) crevice between the epidermis of the free tip of the nucellus and its central core of tissue (fig. 27). The archegonia probably occurred in a ring be- neath this crevice, preparations. Our of L. ovoides from Lomax show the method of formation of this peculiar pollen chamber (figs. 28 and 29). The free beak of the nucellus is covered by an epidermal layer whose cells have thick, resistant walls. Within this layer, near the base of the beak, the thin- walled tissue begins to break down; and this breaking down extends upward beneath the epi- dermis to the apex of the beak, resulting in the characteristic crevice-like pollen chamber surround- ing a central core of tissue. A diagrammatic longitudinal section of the seed is shown in fig. 30; and diagrammatic transverse sections at various levels through the pollen chamber, in figs. 31-34. The contrast of this Lagenostoma method of pollen chamber-formation with the ordi- nary method, such as occurs in the Stephanospermum type of seeds (see below), in the cycads, etc., is striking. In the latter case the pollen chamber begins to develop at the tip of the nucellus and is central; while in Lagenostoma it begins to develop at the base of the nucellar beak and is peripheral. It must be understood, therefore, that the Fig. 28.—Lagenostoma ovoides: longitudinal section of a seed; X12.—From photomicrograph by Land.. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original work.. Coulter, John Merle, 1851-1928; Chamber

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