The New Student's Reference Work/Embryo

From Wikisource
Jump to navigation Jump to search

Em′bryo (in plants), a plant in the earliest stages of its development. In Spermatophytes NSRW Embryo.jpgEmbryo of capsella, showing superior (below) and embryo (above) in various stages of development. the name is restricted to the development within the seed. Taking the bean embryo as an illustration, it consists of a small stem, once called the caulicle, but now known as the hypocotyl, from the lower end of which the root develops, and at the upper end two large and fleshy leaves appear (the halves of the bean), called the cotyledons. Between the cotyledons a little bud is apparent, called the plumule, in which the subsequent leaves are more or less formed, and which is to develop into the shoot when the embryo escapes from the seed. Such an embryo represents the common form among the dicotyledons. Among the monocotyledons, as in corn, the same parts appear, but the single large cotyledon is terminal on the hypocotyl, and the stem tip comes out at one side. Among the conifers, as in pines, a rosette of cotyledons may appear, in the center of which is the plumule. In the development of the embryos of seed-plants a temporary organ, called the suspensor, usually appears. It generally is a more or less elongated filament of cells, which at its tip bears the cell which is to form the real embryo, and by its growth places this cell in a better position in reference to the food-supply which is forming in the seed.

John M. Coulter.