. Botany for high schools and colleges. Botany. 423 BOTANY. 532. Fertilization.—Fertilization takes place as follows : The pollen grain, resting upon the moist surface of the stigma, absorbs moisture and germinates, sending out a tube which penetrates the soft tissues of the stigma and style, finally reaching the cavity of the ovary, where it enters the micropyle of an ovule (Fig. 307, A). Here it comes in con- tact with the apex of the ovule body, through whose tissues it forces its way until it reaches the embryo sac ; in some cases, however, the embryo sac has grown out through the apex of
. Botany for high schools and colleges. Botany. 423 BOTANY. 532. Fertilization.—Fertilization takes place as follows : The pollen grain, resting upon the moist surface of the stigma, absorbs moisture and germinates, sending out a tube which penetrates the soft tissues of the stigma and style, finally reaching the cavity of the ovary, where it enters the micropyle of an ovule (Fig. 307, A). Here it comes in con- tact with the apex of the ovule body, through whose tissues it forces its way until it reaches the embryo sac ; in some cases, however, the embryo sac has grown out through the apex of the ovule body into, and occasionally through the micro- pyle, thus meeting the pollen - tube. The transfer of the con- tents of the pollen- tube to the germ-cell has never been ob- served, but doubtless it takes place by diffu- sion through the pol- len-tube and embryo sac. The first result of fertilization is the formation of a wall of cellulose around the the latter trans-. Fig. 307.—A, a longitudinal section of the anatro- poue ovule of Viola tricolor^ after fertilization, pl^ the placenra; w. the raphe, swollen at this point; a, the outer coat of the ovule ; i, the inner ; », the poi- len-tube which has entered the micropyle ; e, em- bryo sac, with the very young embryo at the micro- pylar end, and numerous free endosperm cells at the other, .ff, apex of embryo sac, e (mnch more mag- nhied); e6, very young embryo of two cells, support- ed by a two-celled suspensor. C, the same, further advanced. All the figures highly magnified.—After gCrm-cell Sachs. ,. , soon divides versely one or more times, and thus gives rise to a row of cells, the suspensor, at the free extremity of which a rudi- mentary embryo is soon formed by the fission of cells in three planes (Fig. 307). Simultaneously with the foregoing ized by Insects ; " " The Eflfecta of Cross and Self-Fertilization in the Vegetable KingdonT;" "Tlie Different Forma of Flowers on Plants of the Sam
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1888
