The description which I have given of the Ovulum of Kingia, though essentially different from the accounts hitherto published of that organ before fecundation, in reality agrees with its ordinary structure in Phaenogamous plants.
I shall endeavour to establish these two points; namely, the agreement of this description with the usual structure of the Ovulum, and its essential difference from the accounts of other observers, as briefly as possible at present; in tending hereafter to treat the subject at greater length, and also with other views.
I have formerly more than once* adverted to the structure of the Ovulum, chiefly as to the indications it affords, even before fecundation, of the place and direction of the future Embryo. These remarks, however, which were certainly very brief, seem entirely to have escaped the notice of those authors who have since written on the same subject.
(*Footnote. Flinders Voyage 2 page 601, and Linnean Society Transactions 12 page page 136.)
In the Botanical Appendix to the account of Captain Flinders' Voyage, published in 1814, the following description of the Ovulum of Cephalotus follicularis is given: Ovulum erectum, intra testam membranaceam continens sacculum pendulum, magnitudine cavitatis testae, and in reference to this description, I have in the same place remarked that, "from the structure of the Ovulum, even in the unimpregnated state, I entertain no doubt that the radicle of the Embryo points to the umbilicus."*
(*Footnote. Flinders Voyage loc. cit.)
My attention had been first directed to this subject in 1809, in consequence of the opinion I had then formed of the function of the Chalaza in seeds;* and sometime before the publication of the observation now quoted, I had ascertained that in Phaenogamous plants the unimpregnated Ovulum very generally consisted of two concentric membranes, or coats, enclosing a Nucleus of a pulpy cellular texture. I had observed also, that the inner coat had no connexion either with the outer or with the nucleus, except at its origin; and that with relation to the outer coat it was generally inverted, while it always agreed in direction with the nucleus. And, lastly, that at the apex of the nucleus the radicle of the future Embryo would constantly be found.
(*Footnote. Linnean Society Transactions 10 page 35.)
On these grounds my opinion respecting the Embryo of Cephalotus was formed. In describing the Ovulum in this genus, I employed, indeed, the less correct term sacculus, which, however, sufficiently expressed the appearance of the included body in the specimens examined, and served to denote my uncertainty in this case as to the presence of the inner membrane.
I was at that time also aware of the existence, in several plants, of a foramen in the coats of the Ovulum, always distinct from, and in some cases diametrically opposite to the external umbilicus, and which I had in no instance found cohering either directly with the parietes of the Ovarium, or with any process derived from them. But, as I was then unable to detect this foramen in many of the plants which I had examined, I did not attach sufficient importance to it; and in judging of the direction of the Embryo, entirely depended on ascertaining the apex of the nucleus, either directly by dissection, or indirectly from the vascular cord of the outer membrane: the termination of this cord affording a sure indication of the origin of the inner membrane, and consequently of the base of the nucleus, the position of whose apex is therefore readily determined.