DEVELOPMENT OF A DICOTYLEDONOUS PLANT. The fertilized egg lies deeply imbedded in the ovary in a sac—the embryo-sae—filled with nu tritive fluid. The fertilized egg. or otlspore, de velops by means of a series of transverse and longitudinal cleavages into a more or less ovoidal body—the embryo. Certain of the cells of the embryo may early become specialized to form a thread composed of a single row of cells and called the suspensor. By means of the suspensor the embryo is pushed out into the nutritive fluids of the embryo-sac. As cell-division pro ceeds a peripheral layer of cells is differentiated, which is the epidermis, also an axial column of cells is often early discernible, with the root-cop cell or cells at the end next to the suspensor, and the stem-tip at the opposite end. The cotyledons an• early formed by a pair of lateral regions of cell-multiplication. In some cases the plumule with its nascent leaves is already formed from t lif• .11•111 lip before germination. The seed may contain the endir?ii as a minute germ iml.g.d41e,1 material tb.rixi•(1 nail the embryo sac pa ri 4 of 11111• once or the teria I may liar.• absorbed liv the online:nut Le 1.11114,11 in Hee cotyledons (beanl.
In I I I 1)1' \II VI OP The egg. laid, is II thing. 'I he shell :Ind albumen ere ,,iilistanecs, laid down a round the egg proper, or 'yellow of the egg,' as it passes along the maternal oviduct. The 'yellow of the egg' is usually while it is still in the oviduct of the hen only a single cell, which is immensely dis tended by food-materials or food-yolk. The nucleus lies in a thin sheet of protoplasm on top of the 'yellow.' This nucleus divides, but the whole yolk does not, so that partial cleavage oc curs, producing a disk of several cells at the time the egg is laid. This disk constitutes the cicatrix, or 'scar' or 'tread' of the egg, which can be readily seen with the naked eye. It is technically called the germ-disk, or blastoderm, and consists of an upper and an under layer. Later a middle layer of cells arises, and the blastoderm is differentiated into a central trans parent area pellucida, on which the embryo forms, and a peripheral arca opuca, which is continuous with the central area and extends laterally until it sourrounds the entire yolk ( Figs. 1-4).