. Botany, with agricultural applications. Botany. FEMALE GAMETOPHYTE 455 extends beyond the nucellus, and its free margin flares open, thus forming an open micropyle that leads into the pollen chamber. Female Gametophyte. — Although four megaspores are formed in the megasporangium, only one of them develops a gameto- phyte, the others being destroyed and used for food by the one that develops. During the first season the surviving megaspore enlarges and becomes multinucleate. With the megaspore in this. Fig. 404. — Development of the ovule and pollen tubes in the Pine. C, section through an ov
. Botany, with agricultural applications. Botany. FEMALE GAMETOPHYTE 455 extends beyond the nucellus, and its free margin flares open, thus forming an open micropyle that leads into the pollen chamber. Female Gametophyte. — Although four megaspores are formed in the megasporangium, only one of them develops a gameto- phyte, the others being destroyed and used for food by the one that develops. During the first season the surviving megaspore enlarges and becomes multinucleate. With the megaspore in this. Fig. 404. — Development of the ovule and pollen tubes in the Pine. C, section through an ovuliferous scale, showing the bract behind and a section of an ovule (s) on its inner face, the megaspore being shown at m; D, an ovule with female gametophyte (/) mature, showing eggs at e, ovule wall consisting of nucellus and integument at w, and pollen grains growing tubes through the nucellus at (p). condition the ovule passes the winter. Early next spring growth is resumed, and by about the first of June of the second season the gametophyte is complete, consisting of 250 or more cells and bearing a number of archegonia (usually two to five) at the micropylar end (Fig. 404-) The eggs are usually ready for fertilization about the first of June of the second season. "While the female gametophyte is developing, the male gametophyte is completing its development in the pollen chamber and the pollen. 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 Martin, John N. (John Nathan), b. 1875. New York, John Wiley & sons, inc. ; [etc. ,etc. ]
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectbotany, bookyear1920
