Page:The New International Encyclopædia 1st ed. v. 07.djvu/47

* EMBRYOLOGY IN PLANTS. 33 EMDEN. the apex of the prothallium develop the stem and leaf structures; those which face the base of the prothallium develop the root and foot structures. The first wall of the fertilized egg, therefore, has had the same general result as the firs! wall of the egg in the case of mosses; that is, it has resulted in separating what may be called the root and shoot structures. In the ferns the development of the young plantlet is continuous, so that the embryo is limited by no special point in time or structure. In Sckkmatoi'iiytes. Among the seed-plants the conditions are quite different. The fertilized egg which lies within the cnil>ryo-sac of the ovule proceeds to germinate at once and to form an embryo of a variable degree of advancement, and t lien the whole process is checked by the final hardening of the seed coats. On account of this the embryo lies dormant for an indefinite period, and when the seed is said to germinate the embryo renews its activity and escapes. In this way it is convenient definitely to mark the embryo as the plantlet that is developed within the seed. As might be expected, such embryos differ very much in the amount of their develop- ment. Some pass into the dormant stage at a very early period in their history, so that they are hardly more than a small indefinite group of cells; others develop several distinct organs, and resemble a well-defined plantlet before pass- ing into the dormant stage. Among seed-plants, while there is considerable variation in the de- tails of germination, the general sequence is as follows: The fertilized egg develops a trans- verse wall, and successive transverse divisions result in a linear row of cells, the cell at one end of the row being anchored to the wall of the embryo-sac. The cell at the free or deeper end of the row is the one which either exclusively or chiefly enters into the formation of the embryo, the rest of the row forming the so-called 'sus- pensor' (q.v. ), which is an organ of the embryo that serves to connect it with the food-supply. In any event, this development of the suspensor results in placing the cell which is to develop the embryo more in the centre of the sac. and hence in a position to be better imbedded in the nutritive tissue. The monocotyledons and dicotyledons are fun- damentally different in the organization of their embryos. In both groups the root-tip is organ- ized at that end of the axis which points toward the mieropyle (the opening left by the integu- ment), and for this reason it is the root-tip that first emerges from the seed. In the ease of the monocotyledons the end of the axis remote from the root-tip organizes the single massive seed-leaf (cotyledon I, while the stem-tip arises laterally, just behind the cotyledon. Naturally in such an embryo there can be but a single cotyledon, and this fact has given name to the group. In the dicotyledons this remote end forms the stem-tip. while the cotyledons appear as lateral members just behind the stem tip. This prevailingly results in two cotyledons, which has suggested the name of the group; but it does not preclude the development of a single cotyledon, or of more than two. For example, this type of embryo belongs to the conifers, where in many eases the cotyledons form a rosette of several members. The regions of the complete dico- tyledonous embryo, which are more easily defined than those of the monocotvledonous embrvo, are as follows: The axis beneath the two cotyledons, at the tip of which is the embryonic root struc- ture, has been named the 'hypocotyl.' This has been variously called "cauliele' and 'radicle,' one name expressing the idea that it is a little stem and the other that it is a little root. It is, however, so peculiar in its structure and power- that it can hardly be called either a distinct stem or a dis- tinel root, so that it has received a name of its EMBRYO : a, of afern; b, ofaliverwort(two-celled) ; c, of aclub-mosa. own. and may be regarded as an organ of the embryo. At the summit of the hypocotyl the two cotyledons occur, variously arranged with ref- erence to one another and to the hypocotyl in the seed. Between the cotyledons, as if continuing the axis, there is often a minute bud called the 'plumule,' which, after the escape of the em- bryo, develops the shoot. For an account of the i scape of the ernbryo, see Seed. EM'BRYOT'OMY (from Gk. Zrfpvov, em- bryov, embryo + to^tj, 1ome, cut, from Tipvav, lemnein, to cut). A division of the foetus into fragments, to extract it by piecemeal, when the narrowness of the pelvis of the mother, or some other faulty conformation, opposes delivery. EM'BTJRY, Philip (1729-75). The first Methodist minister in America. He was born of German parents at Ballygaran, Ireland. Septem- ber 21, 1721). He emigrated to America in 1760. In 1760 he organized a 'class' in New York and began preaching, at first in his own house on Barrack Street, now Park Place, and in 1707 in the rigging loft, on what is now William Street. which has become famous as the cradle of Methodism in the United Statfes. A chapel was built in 1708 on the site of the old John Street Church, partly by Embury's own hands. In 1769 preachers sent out by Wesley arrived in New York, and Embury went as a missionary to the neighborhood of Albany. He continued there as a local preacher and organized a church at Ashgrove. He died from an accident, August, 1775. EMDEN, em'den. A city in the Prussian Province of Hanover, situated on an inlet of the Dollart Bay at the mouth of the Ems. lade Canal and about 75 miles west-northwest of Bremen (Map: Prussia, B 2). It lies low. but is protected by strong dikes from the waters of