. Botany, with agricultural applications. Botany. HOW THE PARTS OF AN OVULE ARE MADE UP 39 surface view of an ovule at two stages of development. Notice how the nuceUus is enclosed by the integuments, leaving only a small openmg at m known as the micropyle. The pollen tube, a tube-like structure produced by the pollen gram m connection with fertihzation, often uses the micropyle as an entrance to the ovule. Some ovules are straight but oftener there is a curving to one side during growth as shown in Figure 44. By curving the micropyle is brought near the base of the ovule, a position more favo
. Botany, with agricultural applications. Botany. HOW THE PARTS OF AN OVULE ARE MADE UP 39 surface view of an ovule at two stages of development. Notice how the nuceUus is enclosed by the integuments, leaving only a small openmg at m known as the micropyle. The pollen tube, a tube-like structure produced by the pollen gram m connection with fertihzation, often uses the micropyle as an entrance to the ovule. Some ovules are straight but oftener there is a curving to one side during growth as shown in Figure 44. By curving the micropyle is brought near the base of the ovule, a position more favorable for the entrance of the pollen tube. How the Parts of an Ovule are made up. ^ The ovule, like all other parts of the plant, is made up of many living units called cells. A cell consists of a mass of living matter called protoplasm, which is generally enclosed by walls. A very important part of the living matter is the nu- cleus, a globular body commonly occupying a central position in the cell. The ovule, although a very small body, is composed of many hundreds of cells, all of which are in some way related to seed formation. The cells of the funiculus, in- teguments, and most of those of the nucellus furnish food and de- velop a covering for the inner and more vita) parts of the seed. In form and structure they are similar to cells composing other parts of the plant. The cells peculiar to the ovule are those forming a special group, usually seven or eight in number and occupying a central position in the nucellus One peculiar feature of these cells is that they usually are not separated by ceU walls and their masses of protoplasm lie in contact or closely join with each other. The region which these cells occupy is known as the embryo sac, so named because within it the embryo develops. The embryo sac, being deeply buried in the nuceUus which is in turn enclosed by the integu- ments, is well protected and to study it the ovule must be sec-. FiG. 46. — Lengthwise sectio
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectbotany, bookyear1920
