repeated division of the four inferior terminal cells, partly by the interstitial growth of those first formed. Soon it bursts through the 104. The growth of the pollen tube, which has been for many months arrested, at last re commences ; the membrane of the summit of the embryo-sac at the same time becomes attenuated, and immediately after is pene trated by the narrowed end of the pollen tube, which is brought into immediate con tact with the summit of the corpusculum, the four cells which previously surmounted it having disappeared. At this time, the corpus culum exhibits in its interior, at the end oppo. site the pollen tube, a single vesicle, much larger than those by which it is surrounded, within which is afterwards developed a se condary cell, occupying more than half its cavity. This cell, which is convex above, is applied by a flattened inferior surface against the wall of the corpusculum. It soon divides by a longitudinal septum into two, each of which is nucleated. These two cells, which occur throughout the Coniferae, form the commencement of the suspensor. They next divide by a second pair of vertical septa, at right angles to the first ; and in each of the four cells which result, a succession of hori zontal septa are formed, by which they are converted into four vertical columns inti mately united to each other. The suspensor lengthens in one direction only, partly by the membrane of the corpusculum at its lower end, and becomes immersed in the tissue which occupies the embryo sac, the cells of which, at the same time, become less intimately united than before. The four series of cells of which the suspensor is formed, now separate, and, from the terminal cell of each, the rudi ment of an embryo takes its origin. Its developrnent commences, like that of the embryos of the Ilepaticm and of the first leaves of the Ferns and Equisetacem, by the repeated formation of alternately inclined septa in a terminal cell ; these being followed by vertical septa radiating from the axis, and, subse quently by others parallel to the external surface. Of the four embryos thus formed, one only advances to vigorous maturity.
105. Phanerogantia angiospermia.—The ob servations on record relating to the origin and development of the embryo among these plants are now so numerous, that although the conditions are much more complicated, and the difficulties in thenaselves much greater, we are, notwithstanding, more competent to draw our conclusions with confidence than we have found ourselves to be in our previous study of the Cryptogamia. Among the many examples at our disposal, we select two of the simplest, between which, at the same time, great differences present themselves in those respects in which the development is variable.
106. Hippuris rulgath.*—The already ana tropous ovule of this plant consists of a cylin drical nucleus of delicate cellular tissue, along one side of which is observed a longitudinal fleshy ridge, terminating above in a short funi culus, by which the ovule is suspended frotn the apex of the one-celled ovary. One of the central cells of this nucleus becomes larger into a tubular superior, and a spheroidal and much smaller inferior compartment. The than the rest, from which it is further distin guished by its containing a free vesicular nu cleolated cell-nucleus and granular fluid. This cell, the embryo sac, rapidly enlarges, and at the same time assumes an elongated oval form. A number of vesicles of various size are de veloped at the same time, at its micropyle extremity, all of vvhich disappear some time before the scattering of the pollen. Shortly after this ha.s taken place several new cells are formed, one of which, situated towards the upper end of the sac, begins at once to lengthen, and is finally converted into a tube closed at both extremities (germ-cell).
The rest arrange themselves in vertical series, so as to form a continuous tissue (the endo sperm), which completely occupies the lower part of the sac. After this, in consequence, as may be presumed, of the contact of the pollen tube with the membrane of the sac, the germ-cell is divided by a transverse septum latter, which is the parent cell of the ernbryo, is divided by a vertical septum into two hemispheres. In these two neNv septa are formed, also vertical, but at right angles to the last. In the meantime, several new vesicles make their appearance in the upper tubular compartment of the germ-cell, which eventually become cylindrical, and arrange themselves, end to end, in its interior. The four cells of the embryo now divide by hori zontal septa, which are succeeded by others parallel to its surface, and meeting their pre decessors at angles of 45°. The globular body which is thus formed, consists of six teen cells, of which eight are superficial, and the other eight enclosed as a central spheri Annals of Natural History : — " The ovule springs from the placental surface as a single projecting cell, which, by subdivision, soon becomes a cellular papilla (the nucleus), com posed of a central cell (the embryo-sac), sur rounded by a simple cellular layer. The two coats gradually grow up over this, and by the greater elongation of one side the ovule becomes anatropous. The nucleus mean hile loses its cellular coat, apparently by absorption, and appears as a large oval sac enclosed in the coats, consisting in fact merely of an embryo sac. In the apex of this, about the epoch when the pollen falls upon the stigma, three cellules (embryonal vesicles), make their appearance at the upper end of cal mass. By the frequent repetition of the same process it increases in size, still retaining its globular form, until it is transformed into an embryo, the direction of growth of the axis of which is downwards.
107, Orchis Morio.— In the Orchidem the structure of the ovule is remarkably simple. The following description of the mode of origin and early development of the embryo, in Orchis Morio, all the stages of which we have ourselves followed, is taken from Mr. Hen frey's paper on Vegetable Reproduction, in the the embryo sac, formed apparently by free cell-formation around a globule of protoplasm. The pollen masses on the stigma send down pollen tubes, which traverse the conducting tissue of the style, and make their way to the placentas, where they enter, ordinarily, singly (sometimes more than one) into the micro pyle canals of the ovules, and come in contact with the outside of the apex of the embryo sac, immediately above where the embryonal vesicles lie ; but the pollen tube does not pene trate the embryo sac. Soon after the pollen tube has reached the embryo sac, one (very rarely two) of the embryonal vesicles begins to swell, becomes divided by a cross septum into two cells, and while the upper one grows out in a filamentous form through the micropyle, by a continued process of cell-division, the lower cell enlarges, and divides repeatedly so as to form a cellular globule—the embryo, which in this plant does not go on to produce a co tyledon and radicle, as in most other cases. The filamentous prolongation, the use of hich is not evident, but which seems ana logous to the suspensor, presently to be rnentioned, meanwhile decays away."* By continuous cell multiplication an organ is formed, in which may be distinguished a 108. 7'he anther and the pollen cell.—The history of the development of the anther is remarkably uniform among the different families of Phanerogamia. It at first appears in the young flower-bud as a cellular papilla, which grows out laterally from the floral axis.