growth and welfare of the subsequent parts of the structure-the bud, the flower, and the seed.

I am sensible that the terms coherent and incoherent do but inadequately express the distinction insisted on between the elaborating or secreting,-and the ministerial non-secreting cellular textures, between the soft pulverulent parenchymatous cells, and the outer membranes of the leaf. The distinction, however, clearly exists in nature, and is important to be borne in mind. I purpose, therefore, in speaking of the anatomical details of the human structure, occasionally to use the word CORPUSCULAR-TEXTURE, as expressive of the soft, friable, parenchymatous textures formed of elaborating cell-organisms, limiting the term CELLULAR-TEXTURE to those which are coherent, nonelaborating, and elastic; for example, the parenchymatous texture of the liver, brain, and intestinal villi, requires to be distinguished from the parenchymatous cellular-texture of the lung.

If adopting this distinction, we extend our microscopical researches to the lower orders of vegetation, we find

1. Forms consisting of incoherent corpuscular textures, masses of cells with an interior granular or viscous, usually green matter;-these are the lowest forms, algæ and lichens, the structure being no more than a light powder, or mucoid and soft.

2. Forms composed of coherent cells, fungi, mosses, and ferns.

3. Forms consisting of the two textures-incoherent cells in the parenchyma, and coherent cells in the cuticle, as in the leaves of phanerogamic plants. The order of vegetable structures, upon this view or classification, may therefore be thus stated.

1. Incoherent corpuscles or cells-(the lowest). 2. Coherent cellular textures-(the next).

3. Incoherent corpuscular, and coherent cellular textures, conjoined, with the addition of stomata, spiral fibres, and woody textures--(the highest).

The last being formed by additions to, and not by superseding the prior forms.

VEGETABLE MORPHOLOGY, which investigates the gradual transformation of the primary cell-elements of the embryo plant into the various special organs of the structure, has long formed an interesting and essential department of physiological botany. The doctrine seems to have originated with Linnæus, was deeply entered on by the celebrated Goëthe, has been universally adopted in Germany, and since received in France and England by most botanists of the present day. The first idea of the subject appeared in the second volume of the tenth edition of the Systema Naturæ in 1759; and in 1760, the propositions were sustained by Linnæus, in a Thesis prepared in the name of his pupil, Ullmark, and called Prolepsis Plantarum. It would be out of place here to enlarge upon botanical facts, regarding the regular metamorphosis of plants which have been firmly established.

"The plan upon which it takes place, is―" according to Dr. Lindley-" notwithstanding the infinite variety observable, extremely simple, and executed by modifications of the leafy (parenchymatous) texture." "There is not only a continuous uninterrupted passage from leaves to bracteæ, from bractea to calyx, from calyx to corolla, from corolla to stamens, and from stamens to pistillum, but there is also," let the reader observe, "a continued tendency on the part of every one of them to revert to the texture, and even to the form of the leaf."*

If the structure of a petal be examined with the microscope, we find a coherent cellular texture abounding with air. The cells of this texture usually contain either a coloured fluid, or numerous active molecules, the cell-walls are irregular in outline, and frequently marked with delicate striæ, and it is evident if the contents of the cells of a petal are formed by a process of metamorphosis from the leafy texture, that it is the green chlorophylle of the parenchymatous cells that has experienced the greatest amount of change;-that is to say, whereas the colour of the leaf is green, and the colour of a petal blue, scarlet, or yellow,—so therefore it must be the green matter-the secreted and proper juices of the leaf-that have experienced the greatest amount of alteration. Again, if the structure of an unripe fruit-the plum or cherry for instancebe examined with the microscope, it is found composed * Introduction to Botany-ante.

of cells filled with numerous green granules, apparently identical with those of the parenchyma of the leaf, but when the fruits are ripe, the cells are filled with coloured fluids of a very different nature,―red, purplish, or yellow, and the green granules have for the most part, or entirely, disappeared.

In this instance, of regular metamorphosis, it is clearly the green chlorophylle of the primary cells that is metamorphosed in the juices of the ripe fruit.

Alterations of form, or diseases, in vegetable structures, rank under the terms irregular and retrograde metamorphosis. Examples of irregular metamorphosis in some part of vegetable structures are innumerable. Roots and tubers exhibit a variety of changes and alterations, chiefly the effects of domestication. The root of the celery is fibrous when wild, but under domestication it becomes round and fleshy like the turnip. In short, leaves, stem, root, flowers, and fruit, exhibit countless irregular metamorphoses, for examples of which the reader is referred to Lindley's Introduction to Botany.

Instances of retrograde metamorphosis are almost equally numerous. The general resemblance of the sepals of the calyx to the ordinary leaves of vegetation is well known; their green colour and tendency to revert into true leaves, is so notorious that it need not be insisted on. In the cowslip and polyanthus, the calyx is frequently formed of five perfect leaves, in no respect different from the others, except in being a

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little smaller. Several instances have been observed in which petals have reverted to the state of sepals and leaves. In a Campanula Rapunculus seen by Röper, the corolla had become five green sepals like those of the calyx; the same was found in an individual of Verbascum pyramidatum, described by Du Petit Thouars. Proliferous flowers of Geum and Rosa, in which the petals had retrograded into leaves, are adduced by Linnæus. In double roses and camellias, the nature of a retrograde metamorphosis is shown in a very instructive way. If any double rose be examined, it will be seen that the filaments of those stamens which stand nearest to the petals, are expanded and coloured like the petals; and sometimes the perfect lobe of an anther will be found on one side the upper margin of the abnormal and expanded filament, and the imperfect remains of another lobe on the opposite side, a convincing proof that the unnatural number of petals has been produced by a retrograde metamorphosis of the stamens. Nothing is more common than to find the pistil converted either into petals or green leaves; in the blackberry roses, and the double cherry, the ovaria have been seen converted into bractea and perfect leaves.* But it is unnecessary to particularize examples, let us therefore

* The year 1845 was remarkable for an absence of fruit on the common bramble, there was hardly a fruited bush to be seen; on examining the abortive flowers, it was found that the seeds and fruit were metamorphosed into bracts.