File:How the Plant Produces Seed (1914) (14591851139).jpg

Identifier: howplantproduces00shar (find matches)
Title: How the Plant Produces Seed
Year: 1914 (1910s)
Authors: Sharp, L.W.
Subjects:
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Contributing Library: Great Smoky Mountains
Digitizing Sponsor: LYRASIS Members and Sloan Foundation

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part of the flower, because thefemale element is borne within it. Within the ovary is a small, rounded body, the ovule. In the youngcherry flower there are two ovules, but usually only one comes tomaturity. The ovule is the part that is to become the seed; thereforeits structure (fig. 97, b) should be studied carefully. It consists primarilyof a central portion surrounded by an envelope, or integument. In thecentral portion is a cavity, the embryo sac, partly filled with cytoplasm.In this sac can be seen several cells with their nuclei; one of these cellsis the egg. An egg is not ordinarily considered so small and simple athing, for the hens egg, with its comparatively large size and elaboratestructure, is perhaps the most familiar type of egg. These features of thehens egg are due, however, to the presence of a large amount of storagematerial and a hard shell, and in the case of a fertile egg to the fact thatat the time it is laid it has already undergone the first stages of develop-
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FlG. 97. MAIN STEPS IN THE DEVELOPMENT OF THE SEED AND THE FRUIT FROM THE FLOWER These diagrams are based in general on the cherry, but, for the sake of clearness, proportions have beensomewhat altered and many unimportant details have been omitted A, Longitudinal section of cherry flower, enlarged 8 diameters. B, Pistil, showing structure of ovuleand development of pollen tubes, enlarged 20 diameters. C, Embryo sac with double fertilization inprocess. D, Development of the embryo from the fertilized egg; the endosperm has developed and filledthe sac. E, Longitudinal section of a nearly ripe cherry, enlarged 8 diameters. When fully mature theendosperm will haye been entirely digested by the embryo, which will fill the seed completely. The seedcoat in the cherry is only a brown papery lining of the pit How the Plant Produces Seed 263 ment into a chick. The real nature of an egg is consequently obscuredin such an example. An egg before fertilization is fundamentally a singlecell, althohowplantproduces00shar

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