"3. The second (1.6.) by short boiling in the caustic alkali is converted into starch, carbonic acid being evolved (granting that starch is the only substance upon which iodine acts so characteristically).

"4. The third (1. c.) by boiling in caustic potash is converted into a peculiar, as yet unknown (?), vegetable principle, which is coloured orange yellow by iodine. Whether in this case carbonic acid be also formed, I will not take upon myself to decide; at least in Experiment VIII., on the addition of sulphuric acid, I did not observe any effervescence. Moreover, this orange colour is as distant as heaven from earth, from the colour produced by adding iodine to vegetable mucus.

"Whether the carbonic acid be formed at the expense of the carbon of the vegetable substance uniting with the oxygen of the air, or by the decomposition of the water, remains still to be investigated; as, likewise, to discover whether by longer boiling, it could take up more carbon, and become converted into oxalic acid.

"The most interesting result is, however, without doubt, that, by the action of the caustic potash, one portion of vegetable matter becomes, by a retrograde metamorphosis, as it were, again converted into starch; a discovery, the extension of which gives promise of most interesting results for organic chemistry."

M. Payen selected with the utmost care the nascent tissue of the ovules of the Almond, Apple, and Sunflower; the halfformed tissue of the Cucumber; the sap of the same plant; the two months' old pith of the Elder; the pith of Æschynomene paludosa; the hairs of Cotton; and the new tissue of spongioles. They gave him the following results :

But when he came to analyse wood in which a deposit had

taken place, he found these proportions materially altered;

the numbers being

When, however, the tissue was acted upon by such agents. as have the property of destroying the matter of lignification, the proportions of the three fundamental principles approached more nearly those of primitive tissue.

With reference to the discrepancy between the first and last of these tables, Payen remarks that, as alkalies do not remove all the matter of lignification, it is possible that this substance may consist of two kinds of matter, one of which only is capable of being acted upon by azotic acid. He also adds that, although concentrated sulphuric acid has the same power as nitric acid of separating from the primitive tissue of plants their sedimentary matter, yet it possesses this difference, that it gives it the property of becoming blue when acted upon by iodine; a circumstance which has doubtless. given rise to the statement that lignine may be transformed into starch. (Comptes rendus, vii. 1055. 1125.)

CHAPTER II.

ELEMENTARY ORGANS.

THE general properties of the elementary organs are, elasticity, extensibility, contractibility, and permeability to fluids or gaseous matter. The first gives plants the power of bending to the breeze, and of swaying backwards and forwards without breaking. The second enables them to develope with great rapidity when it is necessary for them to do so, and also to give way to pressure without tearing. The third causes parts that have been overstrained to recover their natural dimensions when the straining power is removed, and it permits the mouths of wounded vessels to close up so as to prevent the loss of their contents. The fourth secures the free communication of the fluids through every part of a plant which is not choked up with earthy matter.

The special properties of the elementary organs must be considered separately.

That of these the CELLULAR TISSUE is the most important is apparent by its being the only one of the elementary organs which is uniformly present in plants; and by its being the chief constituent of all those compound organs which are most essential to the preservation of species.

It transmits fluids in all directions. In most cellular plants no other tissue exists, and yet in them a circulation of sap takes place; it constitutes the whole of the medullary rays, conveying the elaborated juices from the bark towards the centre of the stem; all the parenchyma in which the sap is diffused upon entering the leaf, and by which it is exposed to evaporation, light, and atmospheric action, consists of cellular tissue; much of the bark in which the descending current of the sap takes place is also composed of it; and in endogenous plants, where no bark exists, there appears to be no other route that the descending sap can take, than through the cellular substance in which the vascular system is em

bedded. It is, therefore, readily permeable to fluid, although it has no visible pores.

In all cases of wounds, or even of the developement of new parts, cellular tissue is first generated: for example, the granulations that form at the extremity of a cutting when embedded in earth, or on the lips of incisions in the wood or bark; the extremities of young roots; scales, which are generally the commencement of leaves; pith, which is the first part created, when the stem shoots up nascent stamens and pistils; ovules; and, finally, many rudimentary parts: in all these at first, or constantly, is formed cellular tissue alone. It is that from which leaf-buds are generated. These organs always appear from some part of the medullary system; when adventitious, from the ends of the medullary rays if developed by stems, or from the parenchyma if appearing upon leaves.

It may be considered the flesh of vegetable bodies. The matter which surrounds and keeps in their place all the ramifications or divisions of the vascular system is cellular tissue. In it the plates of wood of exogenous plants, the woody bundles of endogenous plants, the veins of leaves, and, indeed, the whole of the central system of all of them, are either embedded or enclosed.

The action of fertilisation appears to take place exclusively through its agency. Pollen is only cellular tissue in a particular state; the coats of the anther are composed entirely of it; and the tissue of the stigma, through which fertilisation is conveyed to the ovules, is merely a modification of the cellular. The ovules themselves, with their sacs, at the time they receive the vivifying influence, are a semitransparent congeries of cellules.

It is, finally, the tissue in which chiefly amylaceous or saccharine secretions are deposited. These occur chiefly in tubers, as in the Potato and Arrow-root; in rhizomata, as in the Ginger; in soft stems, such as those of the Sago-Palm and Sugar-cane; in albumen, as that of Corn; in pith, as in the Cassava; in the disk of the flower, as in Amygdalus; and, finally, in the bark, as in all exogenous plants; and cellular tissue is the principal, or exclusive, constituent of these.

In the form of articulated BOTHRENCHYMA, when it is collected together into hollow cylinders, it serves for the rapid transmission of fluids in the direction of the stem; and it is well worth notice, that the size of the tubes of articulated bothrenchyma, and their abundance, are usually in proportion to the length to which the fluid has to be conveyed. Thus in the Vine, Phytocrene, the common Cane, and such plants, the pitted tissue is unusually large and abundant; in ordinary trees much less so; and in herbaceous plants it hardly exists. Bothrenchyma eventually ceases to convey fluid, and becomes filled with air. The use of other kinds of bothrenchyma is not known.

PLEURENCHYMA is apparently destined for the conveyance of fluid upwards or downwards, from one end of a body to another, and for giving firmness and elasticity to every part.

That it is intended for the conveyance of fluid in particular channels seems to be proved: 1. from its constituting the principal part of all wood, particularly of that which is formed in stems the last in each year, and in which fluid first ascends in the ensuing season; 2. from its presence in the veins of leaves where a rapid circulation is known to take place, forming in those plants both the adducent and reducent channels of the sap; and, 3., from its passing downwards from the leaves into the bark, thus forming a passage through which the peculiar secretions may, when elaborated, arrive at the stations where they are finally to be deposited. Knight is clearly of opinion that it conveys fluid either upwards or downwards; in which I fully concur with him: the power of cuttings to grow when inverted seems, indeed, a conclusive proof of this. Dutrochet, however, endeavours to prove that it merely serves for a downward conveyance.

With regard to its giving firmness and elasticity to every part, we need only consider its surprising tenacity, as evinced in hemp, flax, and the like; and its constantly surrounding and protecting the ramifications of the vascular system, which has no firmness or tenacity itself. To this evidence might be added, the admirable manner in which it is contrived to answer such an end. It consists, as has been seen, of lignified slender tubes, each of which is indeed possessed of but a slight degree of strength; but being of different lengths,