any. They are insoluble in alcohol, water, and caustic potash, but are dissolved by nitric acid.

Raphides are found solitary in the cells of Papyrus antiquorum, Epidendrum elongatum, &c., scattered in considerable numbers in the cells of Musa paradisiaca and collected firmly into bundles which are a little shorter than the cells in which they lie. They are in most instances formed in the cells of Merenchyma and Parenchyma without order; but Meyen has observed that in the bark of Viburnum Lantana they are principally stationed in the interior of thin-sided cells, clustered in cavities of thicker sided tissue.

Link compares the raphides in plants to calculi in animals. Raspail asserts that raphides are never found either in Cactus or elsewhere in the inside of the bladders of cellular tissue, but are exclusively placed in the intercellular passages. The slender kind (fig. 13.) he states to be crystals of phosphate of lime, from too of a millimetre in length, and to be in reality six-sided prisms, terminated at each end by a pyramid with the same base. The crystals found in the Cactus and Rhubarb (figs. 11. and 12.), he says are composed of oxalate of lime; and he represents them to be right-angled prisms, terminating in a four-sided pyramid. (Nouv. Syst. de Ch. Org. p. 522.) According to Marquart the raphides of Aloe arborescens consist of phosphoric acid combined with lime and magnesia. Mohl says that raphides are never sixsided prisms, as Raspail asserts; but that they are rightangled four-sided prisms, which gradually vanish into points; and he declares that Meyen is right in asserting that the raphides are constantly formed inside the bladders, and never in the interstitial passages of cellular tissue (Anat. Palm. p. 28.); about which there is no sort of doubt. In Liparis pendula, in which the tissue is very thin, the raphides may be seen in situ without disturbing the surrounding parts, and they then form dense bundles of acicular crystals lying in the centre of cells.

The same circumstance is particularly visible in the oval cells found in the leaves of Caladium esculentum, Dieffenbachia Seguina, and some other Araceæ. Here the acicular raphides are not only collected in bundles inside the cells, but

are expelled from them by an opening at each end of the cell, on which account Turpin calls such cells Biforines. Morren found the power of emitting their raphides preserved in these bodies after having undergone 6° of cold of Reaumur (18° Fahr.), and he therefore concludes that the phenomenon is, as Turpin supposes, a mere physical action produced by endosmose, and not a vital action.

(For further remarks on raphides see the Appendix to this Work.)

SECT. VII. Of amylaceous and other granular matter contained in Tissue.

INSIDE the tissue of plants, are found various kinds of particles, some of which give colour or its peculiar turbid appearance to the fluid, others their nutritive quality to particular species.

Of these some are turned blue by iodine, and are therefore regarded by chemists as composed of amylaceous matter or starch; others are rendered olive brown by that agent, and many are dissolved by alcohol, whence they are considered of the nature of resins: all are decomposed by cold, and appear to be connected with the function of nutrition.

The following kinds may be distinguished:

1. Amylaceous granules.—These are so extremely common that no plant can be said to be destitute of them, and many have the cells of their roots and some parts of their stem filled quite full of them. In the rhizoma of Equisetum the tubes are so crowded with them, that when the tubes are wounded, the granules are discharged with some force, apparently by the contraction of the membrane, so that they appear as if in voluntary motion so long as the emptying the tissue continues to take place. These particles are perfectly white, semitransparent, generally irregularly oblong, sometimes compound, and marked with oblique concentric circles; they are extremely variable in size, some being as fine as the smallest molecular matter in pollen, that is, not more than 3000

of an inch in diameter, others being as much as Too or 730. They often form the centre of the grains of chlorophyll, as Mohl has shown. In the milky juice of Euphorbia, they assume the singular appearance represented at Plate II. fig. 19. b., looking like short cylinders enlarged at each end into a round head: double-headed granules of this kind are not as yet found elsewhere; Morren states that they vary in form in different species of Euphorbia.

Their nature has been carefully investigated by Fritzsche (Ueber das Amylum, Berlin, 1834, and Poggendorf's Annalen, 1834, No. 9, 10.), who has proved them to be formed by the successive deposit of new layers, one over the other, and not to be cells containing soluble matter, as Raspail asserts.

Those which have the smallest size have a distinct motion of rotation when suspended in water; and this motion looks as if spontaneous; for of several floating near each other, in the same medium, a part will be in active motion, while others remain inactive.

Turpin calls these granules Globuline, and considers them the most elementary conditions of vegetable tissue, its primitive form; an opinion which is adopted, with some modifications, by Raspail, who looks upon each granule as one of the elementary molecules of tissue in a state of development. This writer assigns them a point of attachment or hilum, by which they originally adhered to the parent cell: he considers that cellular tissue is produced by the development and mutual pressure of each granule, and that all the varied forms of plants may be explained by reference to this principle. (Nouv. Syst. de Chimie Organique, p. 83.) Morren states that these grains of fecula are the first stage of a crowd of organs, and that he can demonstrate the free spiral thread of Collomia and Salvia to be at first an amylaceous granule. This, however, does not correspond with the statements of Schleiden. Such amylaceous granules appear to have, under particular circumstances, the power of spontaneous growth, by which they multiply and increase themselves externally. This is particularly visible in the fecula of Barley; which, if observed in its original state, is found to be composed of angular, irregular bodies, some of which are of extreme minuteness, and seem

to have a power of spontaneous motion in water. Shortly after germination the amylaceous bodies, according to Turpin, appear to lose their substance, to become more transparent and flaccid, a circumstance which he thinks is owing to the chemical change of their starch into sugar: the granules however at this time retain their property of becoming blue under the action of iodine. When this alteration has been produced, the maltster stops the new chemical action by heat and dryness, and fixes the sugar, as we see in malt. When the amylaceous granules are placed in water of a certain temperature, rendered sweet by the dissolution of their own. sugar, and exposed to the influence of the oxygen of the atmosphere, they evidently produce little sprouts like themselves from their sides. Turpin states that, if examined after fermentation has been going on for some hours, they will be found to have each formed several new granules exactly like the mother-granules; and he not only considers this to be the cause of the curious phenomena observable in fermentation, but regards the granules as seeds and the result of their growth as a plant, which he calls Torula cerevisia. He adds, that in the inside of each of the new granules formed during fermentation, he finds a number of still smaller granules. I have not repeated the observations of this ingenious writer further than to ascertain that the granules in fermentation do sprout; and that they have at that time lost all their starch, for iodine produces no sensible effect upon their colour; a circumstance to which he has not adverted.

According to Schleiden amylaceous granules are gradually changed into gum and mucus in the process of lignification. (Beiträge zur Phytogenesis, p. 17.) This author considers starch to be analogous in plants to the fat in animals. It is nutritious matter in excess, laid by for future use, and is usually found in those places where new organization is about to commence, or where a luxuriance of vegetation has produced an excess of nutriment. Starch is sometimes represented by another half-granular matter, found in pollen, in the albumen of some plants, and abundantly in the Parenchyma of leaves, as the centre of the Chlorophyll. It is especially

distinguished by presenting itself in irregular granular bodies without any internal structure, and becomes brownish yellow or brown when tested with tincture of iodine. This may be called mucus, and appears to be what the Cytoblast and its spherule are composed of. When starch is about to assume a new organization, it converts itself, in some manner unknown to chemists, into sugar or gum.

Sugar makes its appearance as a transparent fluid, which seems as clear as water, is not rendered turbid by alcohol, and is coloured by tincture of iodine, according to the greater or less degree of dilution of that agent.

Gum appears as a yellowish, more consistent, less transparent fluid, which, with tincture of iodine, coagulates into a pale yellow ungranulated colour. When vegetation has advanced to that point that gum is the latest immediate product, there appears in it a great many minute molecules, which are generally so small as to resemble dark points; at that time the fluid becomes a darker yellow upon the application of iodine. But the molecules, if they are large enough to show their colour, become dark-brown yellow. It is this mass, so transparent that it can hardly be seen till it is coloured, in which, in all cases, organization commences, and from which the youngest structure is constituted. may be called Vegetable Jelly, and is probably nearly the same as Pecten, the base of Gum Tragacanth, and many other kinds of vegetable mucus. It is this jelly, which, by a further chemical attraction, becomes the membrane of cells, and is afterwards the material by which it is thickened.

It

2. Chlorophyll or Chromule. To this is referred all the kinds of coloured granules which occupy the interior of vegetable tissue. They have a spheroidal, irregular figure, are often rather angular, consist of a semi-fluid gelatinous substance not contained in a sac, and which seems to be a coagulum of the fluid contents of the cells. The colour of plants, especially the green colour, is produced by the presence of chlorophyll, which may be considered a vital secretion. It will be mentioned more particularly in Book II., in the chapter upon colour.