A practical study of the structure of the ovary is too difficult for the ordinary student to attempt, as it is not easy to cut sections of it which are suitable for microscopical examination. The ovary is mainly composed of soft, thin-walled cells, or parenchyma, which enclose a single ovule surrounded by double walls or integuments (see Fig. 4). The interior of the ovule is occupied by a very large cell called the embryo-sac. Note that the ovule lies free within the ovary except at one point called the funicle, where it is attached to the inner walls of the ovary. The thick walls of the ovary are almost colourless with the a b FIG. 4.-Diagram of a Transverse Section through the Ovary of a Barley Flower. (a) Embryo-sac; (b) Integuments of Ovule; (c) Layer of Cells Containing Chlorophyll; (d) Point of Attachment of Ovule. exception of one layer of cells coloured bright green by chlorophyll; this layer may be easily seen in a transverse section of a fresh ovary. Remove an Anther from the Flower.-Mount it on a slide with water and cover with a thin glass. Observe under the microscope the pollen grains contained within the anther. Dissect out the Lodicules at the Base of the Ovary. Note their exact position within the paleæ with a view to tracing them subsequently in the ripe barley corn. Mount the Lodicules in Water.-Examine them under the microscope, noting their structure and the thin transparent hairs with which they are covered. Again Examine the Spike of Barley in Flower.Observe that on either side of a fully developed flower, and springing from the same internode, is an undeveloped flower sheath about one-third of an inch in length. Close examination will show that this sheath consists of two incompletely developed paleæ. They enclose merely an abortive trace of an ovary, but occasionally fully developed anthers and lodicules are found within the flower sheath. Examine a Spike of Barley collected a few days after Fertilisation.-Note how rapidly the ovaries are increasing in size and tending to fill the space enclosed by the flower sheaths. Fertilisation of the barley flower is effected when pollen grains shed by the anthers come into contact with the stigmata of the ovary. A minute tube carrying a nucleus is extended from a pollen grain into the conducting tissue of the ovary, and after finding its way through the micropyle of the ovule to the embryo-sac, pierces it, leading to fusion of the nuclei of the embryo-sac and pollen grain. After fertilisation has been effected in this manner, the cells within the embryo-sac commence to divide and subdivide, eventually producing the embryo and endosperm of the barley corn to be referred to later on. Fig. 6 is a micro-photograph of a fertilised and developing ovary; note the enlargement of the embryo-sac and the compression of the surrounding walls of the ovule and ovary. Eventually these walls become the thin skins of the barley corn. Compare a Spike of Ripe Two-rowed Barley |