. Elementary botany. Botany. GYMA'OSPERMS: WHITE PINE. 307 as the endosperm. This endosperm continues to grow until a large part of the nucellus is consumed for food. 623. Female prothallium and archegonia.âThe endosperm is the female prothallium. This is very evident fnjm the fart that severa. archegonia are developed in it usually on the side toward the pollen chamber. The archegonia are orgtms, and since the sexual organs are developed on the gametophyte, therefore, the endosperm is the female gamctophyte, or prothallium. In fig. 359 are repjresented two archegonia in the endosperm
. Elementary botany. Botany. GYMA'OSPERMS: WHITE PINE. 307 as the endosperm. This endosperm continues to grow until a large part of the nucellus is consumed for food. 623. Female prothallium and archegonia.âThe endosperm is the female prothallium. This is very evident fnjm the fart that severa. archegonia are developed in it usually on the side toward the pollen chamber. The archegonia are orgtms, and since the sexual organs are developed on the gametophyte, therefore, the endosperm is the female gamctophyte, or prothallium. In fig. 359 are repjresented two archegonia in the endosperm and the pollen tubes are growing down through the nucellus. The arche- gonia are quite large, the wall is a sheath or jacket of cells \vhich encloses the very large egg which has a large nucleus in the center. 624. Pollen tube and sperm cells.âWhile the endosperm (female pro- thallium) and archegonia arc dcvelo]>i[Tg the jjollen tube continues its growth down through the nucellar cap, as shown in tig. 359. At the same time the two cells which were formed in the pollen grain (antheridium) from the central cell move down into the tube. < )ne of these is the "generative" cell, or "body" cell, and the other is called the stalk (.l'11, though it is more propjerly a sterile half of the central cell. The nucleus of the gener- ative cell, about the time the archegonium is mature, divides to form two nuclei, which are the sperm nuclei, and the one in advance is the larger, though it is much smaller than the egg nucleus. 625. Fertilization.âA'ery soon after the archegonia are mature (early in June in the northern Ignited States) ihc pollen tuVje grows through into the archegonium and empties the two sperm nuclei, the vegctati\'e nucleus and the stalk cell, into the proto- plasm of the large egg. The larger of the two sperm nuclei at once comes in contact with the very large egg nucleus and sinks down into a depression of the same, as sho\\'n in hg. 361. These
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