ders. Of this nature are the reticulated cells of the seed-coat of Maurandya Barclayana, Wightia gigantea, and the like. (Plate I. fig. 11.)

3. Fibres running spirally close together, except at certain places where they separate and leave between them small spaces, which appear like dots.

4. Fibres running spirally, but completely grown together, except at certain spaces where they separate and leave small dot-like spaces. This and the last have been noticed by Mr. Valentine in Orchidaceous plants, and have been extremely well figured by Slack. (Trans. Soc. Arts, vol. xlix. t. 6. f. 5, 6.)

5. Fibres running straight along the sides of truncated cylindrical cells in the anthers of Richardia africana (Calla æthiopica) and many other plants. (Plate I. fig. 13.) 6. Fibres running transversely in parallel lines round three of the sides of prismatical right-angled cells, in the anthers of Nymphæaceæ, &c.

7. Fibres very short, attached to the sides of cells of various figures, to which they give a sort of toothed appearance, as in the anther of Phlomis fruticosa and other Labiatæ. (Plate I. fig. 15.)

The last three were first noticed by Purkinje.

8. The fibre twisted spirally, in the membranous tubes that form the elaters of Jungermannia, apparently constitutes another form of tissue of this order (Plate I. fig. 17.), and has recently been found by Corda among Fungi in the genus Trichia.

B. Fibre without Membrane.

It is not improbable that this form is always in the beginning of its growth composed of membrane. Mirbel has shown that the curious cells which line the anther of the common gourd are continuous membranes till just before the expansion of the flower, when they very suddenly enlarge, and their sides divide into narrow ribands or threads, curved in almost elliptical rings which adhere to the shell of the anther by one end; these rings are placed parallel with each other in each

C

.

cell, to which they give an appearance like that of a little gallery with two rows of pilasters, the connecting arches of which remain after the destruction of the roof and walls. According to the observations of Dr. Schleiden, the formation of fibre never takes place independently of membrane, but occurs in the interior of cells, whose membrane was originally quite simple. He regards Corda's statements to the contrary (Ueber Spiralfaserzellen, 7. and 8.), as formed upon imperfect observations. He says that cells always attain their full size before the fibre appears, and he regards its formation as a part of the process of lignification. In the beginning he states that each cell is filled with starch, rarely with mucus or gum. By degrees the starch is always converted into the latter; this becomes changed, and, as it would seem, always from without inwards, into jelly. This jelly changes at its surface into a spiral fibre of variable width, which either does or does not adhere to the sides of the cells, and which may be supposed to owe its spiral direction to the course taken by a current setting between the side of the cell and the central mass of jelly.

The following are the more important varieties: —

1. Spiral fibres repressed by mucus, but having sufficient elasticity to uncoil when the mucus is dissolved, and then breaking up into rings. (Plate I. fig. 16.) These are what are found in the seed-coat of Collomia linearis. They approach ⚫ spiral vessels so very nearly, that when I originally discovered them I mistook them for such. They are known by their depressed figure when at rest, by the want of an inclosing membrane, and by their brittleness when uncoiled.

2. Fibres short, straight, and radiating, so as to form little starlike appearances, found in the lining of the anthers of Polygala Chamæbuxus, &c. by Purkinje. (Plate I. fig. 19.)

3. Fibres originating in a circle, curving upwards into a sort of dome, and uniting at the summit, observed by the same anatomist in the anthers of Veronica perfoliata, &c.

4. Fibres standing in rows, each distinct from its neighbour, and having its point hooked, so that the whole has some resemblance to the teeth of a currycomb, in the anthers of Campanula; first noticed by Purkinje. (Plate I. fig. 18.)

5. Fibres forming distinct arches, as seen in the anthers of Linaria cymbalaria, &c. by Purkinje. (Plate I. fig. 4.)

In the centre of some of the bladders of the cellular tissue of many plants there is a roundish nucleus, apparently consisting of granular matter, the nature of which is unknown. It was originally remarked by Francis Bauer, in the vesicles of the stigma of Phaius Tankervilliæ. A few other vegetable anatomists subsequently noticed its existence; and Brown, in his Memoir on the mode of impregnation in Orchidacea and Asclepiadaceæ, has made it the subject of more extended observation. According to this botanist, such nuclei not only occasionally appear on the cuticle of some plants (Plate III. fig. 9.), in the pubescence of Cypripedium and others, and in the internal tissue of the leaves, but also in the cells of the ovule before impregnation. It would seem that Brown considers stomates to be formed by the juxtaposition of two of these nuclei. (See also Slack, in the Trans. Soc. Arts, xlix.)

Dr. Schleiden has published some extremely interesting observations upon this body, which he regards as a universal elementary organ, and calls Cytoblast.+ According to this observer, the form varies from oval to lenticular and round, the colour from yellowish to a silvery white, and changing to pale yellow up to darkest brown upon the application of iodine in size it varies between go of a Paris inch in diameter, in Fritillaria pyrenaica, where it attains its largest size, and Tʊʊʊ in the embryonal end of the pollen tube of Linum pallescens. In structure it is usually granular; in consistence it varies between extreme softness and such a degree of toughness, as enables it to resist the pressure of the compressorium without altering its form. In the interior of the Cytoblast, or sunk in its surface, is a small, well-defined

* According to the last mentioned author, the fibres themselves are generally tubular, and either perfectly round or somewhat compressed, or even three or four sided. He considers it proved that they are hollow, by their appearance when compressed, by their occasionally containing bubbles of air, and by the difference between their state when dried and when

recent.

+ I regret very much that my imperfect acquaintance with the German language is insufficient to enable me to give the valuable observations of this excellent observer more in detail.

body, which, to judge from its shadow, represents a thick ring or a thick-sided hollow spherule: there is generally but one such spherule to each Cytoblast, but occasionally there are two or even three. The spherule varies in size from half the diameter of the Cytoblast to a point too small to be measured; and Dr. Schleiden has ascertained that this minute body is formed earlier than the Cytoblast itself. It is sometimes darker, sometimes clearer than the rest of the Cytoblast; and is usually of a firmer consistence, remaining well defined when the latter is crushed by pressure into amorphous mucus.

If the gum which is found in the youngest albumen of a plant be examined, it will be found turbid with molecules of extreme minuteness. Of these some acquire a larger size and a more definite outline than others, and by degrees Cytoblasts appear, which seem to be a granular coagulation round each molecule. As soon as the Cytoblast has attained its full size, there appears upon it a fine transparent vesicle; this is a young cell, which at first represents a very flat segment of a sphere whose flat side is formed of the Cytoblast and convex side of the young vesicle, which is fixed upon it like the half of an hour-glass (wie ein Uhrglas auf einer Uhr). The space lying between the convexity of the vesicle and the Cytoblast is as clear and transparent as water, and is apparently filled with an aqueous fluid. If these young cells are isolated, we may, by shaking the field of the microscope, wash the mucous molecules almost clean; but they cannot be long observed, because they dissolve in distilled water in a few minutes, and leave nothing but the Cytoblast behind. The vesicles continue to swell out, and their lining becomes formed of jelly, with the exception of the Cytoblast, which soon becomes a part of their wall: the cell keeps increasing in size, till at last the Cytoblast is only a minute body imbedded in the side of the cavity, or sometimes loose in the cavity. It is, however, in time absorbed, and it is only after its absorption has occurred that, as Schleiden believes, the process of depositing secondary layers begins. The Cytoblast appears, however, sometimes to have a permanent existence, as in the pollen of Larix europæa, and in those hairs in which a circulation of

the sap is observable. In those Schleiden has remarked (and my own observations coincide with his) that all the currents proceed from the Cytoblast and return to it.

SECT. II. Of Pitted Tissue, or Bothrenchyma.

THIS, which has had a variety of names, (Tubes poreux, Vaisseaux en chapelet, Tubes corpusculiferes, Vasiform Tissue, Dotted Ducts,) consists of tubes, often of considerable size, appearing when viewed by transmitted light as if riddled full of holes. Upon a more accurate inspection, however, it is found to receive that appearance from its sides being filled with little pits sunk in the thickness of the lining. (See Plate II. fig. 2.) Of this there are two kinds.

1. Articulated Bothrenchyma.-This is very common in wood. The holes which are so evident to the naked eye, in a transverse section of the oak or the vine, are its mouths; and the large openings in the ends of the woody bundies of Monocotyledonous stems, as in the Cane, are also almost always caused by the section of it. The stems of Arundo Donax, or of any larger grass, is an excellent subject for seeking it in; it can be readily extracted from them when boiled. It is composed of truncated cylinders, placed one upon the other, and so forming a long cylinder, which be

*Bo@poc, a little pit.