. Elementary botany . Botany. OVULE 8S to the funicle (figs. 109, 112). (3) A campylotropous ovule is one in which the nucellus is itself curved; often it is kidney- shaped (figs, no, 113). FERTILISATION AND CHANGES IN THE OVULE. When a healthy pollen-grain reaches a suitable stigma (fig. 114 sg) it germinates by sending a slender tube {pt) down the style. The end of this pollen-tube eventually enters the micropyle (w), and comes into contact with the nucellus close to the top of the embryo-sac (es).* The consequence of fertilisation is that the ovule grows and becomes a seed (compare figs. 11
. Elementary botany . Botany. OVULE 8S to the funicle (figs. 109, 112). (3) A campylotropous ovule is one in which the nucellus is itself curved; often it is kidney- shaped (figs, no, 113). FERTILISATION AND CHANGES IN THE OVULE. When a healthy pollen-grain reaches a suitable stigma (fig. 114 sg) it germinates by sending a slender tube {pt) down the style. The end of this pollen-tube eventually enters the micropyle (w), and comes into contact with the nucellus close to the top of the embryo-sac (es).* The consequence of fertilisation is that the ovule grows and becomes a seed (compare figs. 114 and 115). The most important change in the ovule is that a minute new plant—the embryo— develops inside the embryo-sac. The " embryo-sac grows and becomes, wholly J. a; or partially, filled with endosperm, which surrounds the embryo. This endosperm may be present still in the seed, and Fig. 114.—Vertical section ^^ ^eed IS Said p,f through a carpel and an anatro- tO be endospermic pous ovule, showing the pollen- ^ A ti' tube entering the micropyle. ^S- VjraSS anu Violet (figs. 118, wi? 158). Or the endosperm formed in the ovule may be gradually absorbed by the growing embryo, so that in the ripe seed there remains no trace of it: , ^>. "1,1 _7. i-"^ jDuiLeruup, Willi ui the seed is then said to be 7ion-enaosper- anatropous seed: per Bean and Wallflower (fig. 116). ^:^^,iJ:='^^^^^Z. In most flowering plants, whilst the em- bryo-sac, the contained endosperm, and the embryo are grow- * This process can only be followed properly by the aid of a compound microscope. In a few Angiosperms the pollen-tube does not enter by the micropyle, but pushes its way through the substance of the ovule till it reaches the embryo-sac. In the Pine and Gymnosperms the pollen- grain itself reaches the micropyle and then sends out a Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - color
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectbotany, bookyear1898
