. Agricultural botany, theoretical and practical. Botany, Economic; Botany. 274 REPRODUCTION on the stigma of the carpel of a suitable flower it germinates and produces a pollen-tube which penetrates into the tissues of the stigma and grows down through the style into the cavity of the ovary: the time taken to reach this point may vary from a few hours to several weeks, according to the kind of plant. ^ The advancing pollen-tube is guided in some way not com- pletely understood into the micro- pyle of the ovule and at length comes into contact with the apex of the embryo-sac close to the egg-
. Agricultural botany, theoretical and practical. Botany, Economic; Botany. 274 REPRODUCTION on the stigma of the carpel of a suitable flower it germinates and produces a pollen-tube which penetrates into the tissues of the stigma and grows down through the style into the cavity of the ovary: the time taken to reach this point may vary from a few hours to several weeks, according to the kind of plant. ^ The advancing pollen-tube is guided in some way not com- pletely understood into the micro- pyle of the ovule and at length comes into contact with the apex of the embryo-sac close to the egg- apparatus (Fig. 99). On reaching this point its tip becomes dis- organised and one of the genera- tive cells of the pollen-grain travels on through the open end of the tube until it meets the ovum or oosphere. The generative cell and ci_^ the ovum then fuse into one, their parts becoming completely inter- mingled. This fushion of a genera- tive cell with the ovum is the essen- tial feature of the sexual act and is spoken oS. 2& fertilisation. In several instances the second generative nucleus from the poUen- the arrangement of the various parts groin has rerpntiv hppn fniinH tn at the time of fertilisation, o Ovary; 6^'^'" ""^^ recently Oeen lOUnU 10 fuse similarly with the definitive nucleus in the embryo-sac, and this ' double fertilisation process' is pro-. Fig. gg.—Diagramof a longitudinal sectioniof a carpel containing an ortho- tropous ovule: designed to illustrate style; st stigma of the carpel; p pollen-grain germinated on the stigma ; pt pollen-tube; r the genera- tive nucleus ; / funicle; ch chalaza ; c integuments of ovule ; « nucellus ; es embryo-sac; e ovum or egg-cell; ^definitive nucleus; a antipodal cells, bably gcneralamongfloweringplants. Unless the ovum is fertilised both it and the whole ovule wither and die, but as Soon as fertilisation is effected the ovum com- mences to divide and grow, developing into an embryo plant, the whole ovul
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
