. A textbook of botany for colleges and universities ... Botany. Fics. 525,526. — Cndtim lalifolium: 525, branches bearing ovulate stroliili; 526, part of o\'Lilatc strobilus. — After Blujie. of swimming sperms. In Ephedra a remarkable funnel-shaped jxillen chamber is developed by the break- ing down of the nucellar tissue (fig. 528), which extends to the embryo sac and the neclcs of the archegonia; hence in pollination the pollen grains may come to rest in contact with the archegonium necks. In Gnetum the tip of the nucellus is more or less disorgan- ized, and this is the only trace
. A textbook of botany for colleges and universities ... Botany. Fics. 525,526. — Cndtim lalifolium: 525, branches bearing ovulate stroliili; 526, part of o\'Lilatc strobilus. — After Blujie. of swimming sperms. In Ephedra a remarkable funnel-shaped jxillen chamber is developed by the break- ing down of the nucellar tissue (fig. 528), which extends to the embryo sac and the neclcs of the archegonia; hence in pollination the pollen grains may come to rest in contact with the archegonium necks. In Gnetum the tip of the nucellus is more or less disorgan- ized, and this is the only trace of a pollen chamber (fig. 530); while in Tiiiiihoa there is not e\'en a trace. Female gametophyte. —The struc- ture hytc in Gnetales is of great interest, for there is an evident apiproach t<i- pj,, wards the angiosperm condition. Ovule. — The ovule has two integuments, the inner one forming a long tubular micropyle, which is a marked feature of the group (figs. 521, 528, 530). The nucellus has the usual gymnosperm feature of a heavy mass of sterile tissue overlying the megaspore mother cell (and later the embryo sac). In all the preceding groups of gymno- sperms, except Coniferales, this overlying tissue is beaked and contains a pollen chamber, a structure associated with the presence. 5 = 7-- - Ovulate .strobili of Gnrtiim, with Ifebhy beeiJs maturing. 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 Coulter, John Merle, 1851-1928; Barnes, Charles Reid, 1858-1910, joint author; Cowles, Henry Chandler, 1869- joint author. New York, Cincinnati [etc] American book company
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