Volume I Part 33 (1/2)
_Love out their hour and leave their lives in air._
CANTO IV. l. 456.
From the accurate experiments and observations of Spallanzani it appears that in the Spartium Junceum, rush-broom, the very minute seeds were discerned in the pod at least twenty days before the flower is in full bloom, that is twenty days before fecundation. At this time also the powder of the anthers was visible, but glued fast to their summits. The seeds however at this time, and for ten days after the blossom had fallen off, appeared to consist of a gelatinous substance. On the eleventh day after the falling of the blossom the seeds became heart- shape, with the basis attached by an appendage to the pod, and a white point at the apex; this white point was on pressure found to be a cavity including a drop of liquor.
On the 25th day the cavity which at first appeared at the apex was much enlarged and still full of liquor, it also contained a very small semi- transparent body, of a yellowish colour, gelatinous, and fixed by its two opposite ends to the sides of the cavity.
In a month the seed was much enlarged and its shape changed from a heart to a kidney, the little body contained in the cavity was increased in bulk and was less transparent, and gelatinous, but there yet appeared no organization.
On the 40th day the cavity now grown larger was quite filled with the body, which was covered with a thin membrane; after this membrane was removed the body appeared of a bright green, and was easily divided by the point of a needle into two portions, which manifestly formed the two lobes, and within these attached to the lower part the exceedingly small plantule was easily perceived.
The foregoing observations evince, 1. That the seeds exist in the ovarium many days before fecundation. 2. That they remain for some time solid, and then a cavity containing a liquid is formed in them. 3. That after fecundation a body begins to appear within the cavity fixed by two points to the sides, which in process of time proves to be two lobes containing a plantule. 4. That the ripe seed consists of two lobes adhering to a plantule, and surrounded by a thin membrane which is itself covered with a husk or cuticle. Spalanzani's Dissertations, Vol.
II. p. 253.
The a.n.a.logy between seeds and eggs has long been observed, and is confirmed by the mode of their production. The egg is known to be formed within the hen long before its impregnation; C.F. Wolf a.s.serts that the yolk of the egg is nourished by the vessels of the mother, and that it has from those its arterial and venous branches, but that after impregnation these vessels gradually become impervious and obliterated, and that new ones are produced from the fetus and dispersed into the yolk. Haller's Physiolog. Tom. VIII. p. 94. The young seed after fecundation, I suppose, is nourished in a similar manner from the gelatinous liquor, which is previously deposited for that purpose; the uterus of the plant producing or secreting it into a reservoir or amnios in which the embryon is lodged, and that the young embryon is furnished with vessels to absorb a part of it, as in the very early embryon in the animal uterus.
The sp.a.w.n of frogs and of fish is delivered from the female before its impregnation. M. Bonnet says that the male salamander darts his s.e.m.e.n into the water, where it forms a little whitish cloud which is afterwards received by the swoln a.n.u.s of the female, and she is fecundated.--He adds that marine plants approach near to these animals, as the male does not project a fine powder but a liquor which in like manner forms a little cloud in the water.--And further adds, who knows but the powder of the stamina of certain plants may not make some impression on certain germs belonging to the animal kingdom! Letter XLIII. to Spalanzani, Oevres Philos.
Spalanzani found that the seminal fluid of frogs and dogs even when diluted with much water retained its prolific quality. Whether this quality be simply a stimulus exciting the egg into animal action, which may be called a vivifying principle, or whether part of it be actually conjoined with the egg is not yet determined, though the latter seems more probable from the frequent resemblance of the fetus to the male parent. A conjunction however of both the male and female influence seems necessary for the purpose of reproduction throughout all organized nature, as well in hermaphrodite insects, microscopic animals, and polypi, and exists as well in the formation of the buds of vegetables as in the production of their seeds, which is ingeniously conceived and explained by Linneus. After having compared the flower to the larva of a b.u.t.terfly, confining of petals instead of wings, calyxes instead of wing-sheaths, with the organs of reproduction, and having shewn the use of the farina in fecundating the egg or seed, he proceeds to explain the production of the bud. The calyx of a flower, he says, is an expansion of the outer bark, the petals proceed from the inner bark or rind, the stamens from the alburnum or woody circle, and the style from the pith.
In the production and impregnation of the seed a commixture of the secretions of the stamens and style are necessary; and for the production of a bud he thinks the medulla or pith bursts its integuments and mixes with the woody part or alburnum, and these forcing their pa.s.sage through the rind and bark const.i.tute the bud or viviparous progeny of the vegetable. System of Vegetables translated from Linneus, p. 8.
It has been supposed that the embryon vegetable after fecundation, by its living activity or stimulus exerted on the vessels of the parent plant, may produce the fruit or seed-lobes, as the animal fetus produces its placenta, and as vegetable buds may be supposed to produce their umbilical vessels or roots down the bark of the tree. This in respect to the production of the fruit surrounding the seeds of trees has been a.s.similated to the gall-nuts on oak-leaves, and to the bedeguar on briars, but there is a powerful objection to this doctrine, viz. that the fruit of figs, all which are female in this country, grow nearly as large without fecundation, and therefore the embryon has in them no self-living principle.
NOTE x.x.xIX.--VEGETABLE GLANDULATION.
_Seeks, where fine pores their dulcet balm distil._
CANTO IV. l. 503.
The glands of vegetables which separate from their blood the mucilage, starch, or sugar for the placentation or support of their seeds, bulbs, and buds; or those which deposit their bitter, acrid, or narcotic juices for their defence from depredations of insects or larger animals; or those which secrete resins or wax for their protection from moisture or frosts, consist of vessels too fine for the injection or absorption of coloured fluids, and have not therefore yet been exhibited to the inspection even of our gla.s.ses, and can therefore only be known by their effects, but one of the most curious and important of all vegetable secretions, that of honey, is apparent to our naked eyes, though before the discoveries of Linneus the nectary or honey-gland had not even acquired a name.
The odoriferous essential oils of several flowers seem to have been designed for their defence against the depredations of insects, while their beautiful colours were a necessary consequence of the size of the particles of their blood, or of the tenuity of the exterior membrane of the petal. The use of the prolific dust is now well ascertained, the wax which covers the anthers prevents this dust from receiving moisture, which would make it burst prematurely and thence prevent its application to the stigma, as sometimes happens in moist years and is the cause of deficient fecundation both of our fields and orchards.
The universality of the production of honey in the vegetable world, and the very complicated apparatus which nature has constructed in many flowers, as well as the acrid or deleterious juices she has furnished those flowers with (as in the Aconite) to protect this honey from rain and from the depredations of insects, seem to imply that this fluid is of very great importance in the vegetable economy; and also that it was necessary to expose it to the open air previous to its reabsorption into the vegetable vessels.
In the animal system the lachrymal gland separates its fluid into the open air for the purpose of moistening the eye, of this fluid the part which does not exhale it absorbed by the puncta lachrymalia and carried into the nostrils; but as this is not a nutritive fluid the a.n.a.logy goes no further than its secretion into the open air and its reabsorption into the system; every other secreted fluid in the animal body is in part absorbed again into the system, even those which are esteemed excrement.i.tious, as the urine and perspirable matter, of which the latter is secreted, like the honey, into the external air. That the honey is a nutritious fluid, perhaps the most so of any vegetable production, appears from its great similarity to sugar, and from its affording sustenance to such numbers of insects, which live upon it solely during summer, and lay it up for their winter provision. These proofs of its nutritive nature evince the necessity of its reabsorption into the vegetable system for some useful purpose.
This purpose however has as yet escaped the researches of philosophical botanists. M. Pontedera believes it designed to lubricate the vegetable uterus, and compares the horn-like nectaries of some flowers to the appendicle of the caec.u.m intestinum of animals. (Antholog. p. 49.) Others have supposed that the honey, when reabsorbed, might serve the purpose of the liquor amnii, or white of the egg, as a nutriment for the young embryon or fecundated seed in its early state of existence. But as the nectary is found equally general in male flowers as in female ones; and as the young embryon or seed grows before the petals and nectary are expanded, and after they fall off; and, thirdly, as the nectary so soon falls off after the fecundation of the pistillum; these seem to be insurmountable objections to both the above-mentioned opinions.
In this state of uncertainty conjectures may be of use so far as they lead to further experiment and investigation. In many tribes of insects, as the silk-worm, and perhaps in all the moths and b.u.t.terflies, the male and female parents die as soon as the eggs are impregnated and excluded; the eggs remaining to be perfected and hatched at some future time. The same thing happens in regard to the male and female parts of flowers; the anthers and filaments, which const.i.tute the male parts of the flower, and the stigma and style, which const.i.tute the female part of the flower, fall off and die as soon as the seeds are impregnated, and along with these the petals and nectary. Now the moths and b.u.t.terflies above-mentioned, as soon as they acquire the pa.s.sion and the apparatus for the reproduction of their species, loose the power of feeding upon leaves as they did before, and become nourished by what?--by honey alone.
Hence we acquire a strong a.n.a.logy for the use of the nectary or secretion of honey in the vegetable economy, which is, that the male parts of flowers, and the female parts, as soon as they leave their fetus-state, expanding their petals, (which const.i.tute their lungs,) become sensible to the pa.s.sion, and gain the apparatus for the reproduction of their species, and are fed and nourished with honey like the insects above described; and that hence the nectary begins its office of producing honey, and dies or ceases to produce honey at the same time with the birth and death of the stamens and the pistils; which, whether existing in the same or in different flowers, are separate and distinct animated beings.
Previous to this time the anthers with their filaments, and the stigmas with their styles, are in their fetus-state sustained by their placental vessels, like the unexpanded leaf-bud; with the seeds existing in the vegetable womb yet unimpregnated, and the dust yet unripe in the cells of the anthers. After this period they expand their petals, which have been shewn above to const.i.tute the lungs of the flower; the placental vessels, which before nourished the anthers and the stigmas, coalesce or cease to nourish them; and they now acquire blood more oxygenated by the air, obtain the pa.s.sion and power of reproduction, are sensible to heat, and cold, and moisture, and to mechanic stimulus, and become in reality insects fed with honey, similar in every respect except their being attached to the tree on which they were produced.