Mr. Brown to the knowledge that previously existed, consisted in the discovery of the presence of two kinds of active particles in pollen, of which one is spheroidal, extremely minute, and not distinguishable from the moving ultimate organic particles common to all parts of a vegetable, the other much larger, often oblong, and unlike any other kind of particle hitherto detected in plants.

The supposed functions of these particles will be explained hereafter. For the present it will be sufficient to remark, that some of the best subjects in which to witness their motions are Clarkia pulchella, Mirabilis jalapa, and Lolium

perenne.

The stamen deviates in a greater degree than any other organ from the structure of the leaf, from a modification of which it is produced; and, at first sight, in many cases, it appears impossible to discover any analogy between the type and its modification; as, for instance, between the stamen and leaf of a Rose. Nevertheless, if we watch the transitions that take place between the several organs in certain species, what was before mysterious or even inscrutable, becomes clear and intelligible. In Nymphæa alba the petals so gradually change into stamens, that the process may be distinctly seen to depend upon a contraction of the lower half of a petal into the filament, and by a development of yellow matter within the substance of the upper end of the same petal on each side into pollen. A similar kind of passage from petals to stamens may be found in Calycanthus, Illicium, and many other plants. Now, as no one can doubt that a petal is a modified leaf, it will necessarily follow, from what has been stated, that a stamen is one also. But it is not from parts in their normal state that the best ideas of the real nature of the stamen may be formed; it is rather by parts in a monstrous state, when reverting to the form of that organ from which they were transformed, that we can most correctly judge of the exact nature of the modification. Take for example that wellknown double Rose, called by the French R. Eillet. In that very remarkable variety, the unguis of the petals may at all times be found in every degree of gradation from its

common state to that of a filament, and the lamina sometimes almost of its usual degree of developement, — sometimes contracting into a lobe of the anther on one side, or perhaps on both sides, now having the part assuming the character of the anther merely yellow, now polliniferous, and finally acquiring, in many instances, all the characters of an undoubted though somewhat distorted stamen. Double Pæonies, Double Tulips, and many other monstrous flowers, particularly of an icosandrous or polyandrous structure, afford equally instructive specimens. It is for these reasons that it is stated in the Outlines of the first Principles of Botany, 307., that "the anther is a modification of the lamina, and the filament of the petiole."

Such is the structure of the stamens in their perfect state. It often, however, happens that, owing to causes with which we are unacquainted, some of the stamens are developed imperfectly, without the anther and pollen. In such cases they are called sterile stamens, and are frequently only to be recognised by the position they bear with respect to the other parts of the flower. Botanists consider every appendage, or process, or organ, that forms part of the same verticillus of organs as the true stamens, or that originates between them and the pistillum, as stamens, or as belonging to what Röper calls the androcæum, namely, to the male system; and every thing on the outside of the fertile stamens is in like manner usually referred to modifications of petals; a remarkable instance of which is exhibited by Passiflora. The appearances assumed by these sterile stamens are often exceedingly curious, and generally extremely unlike those of the fertile stamens: thus in Canna they are exactly like the petals; in Hamamelis they are oblong fleshy bodies, alternating with the fertile stamens; in Pentapetes they are filiform, and placed between every three fertile ones; in Scitamineæ they are minute gland-like corpuscles, a very common form (Plate IV. fig. 10. c); in Brodiæa they are bifid petaloid scales; and in Asclepiadea they undergo yet more remarkable transformations. M. Dunal calls these sterile stamens lepals (lepala); a term which has not yet been adopted.

9. Of the Disk.

By this term are meant certain bodies or projections, situated between the base of the stamens and the base of the ovarium, but forming part with neither; they are referred by the school of Linnæus, along with other things, to nectarium: Link calls them sarcoma and perigynium; and Turpin, phycostemones. The most common form is that of a fleshy ring, either entire or variously lobed, surrounding the base of the ovarium (Plate V. fig. 4. e, 8. d), as in Lamium, Cobæa, Gratiola, Orobanche, &c.; in Gesneries and Proteaceæ the disk consists of fleshy bodies of a conical figure, which are usually called glandulæ hypogynæ. It occasionally assumes the appearance of a cup, named by M. De Candolle in Pæonias and Aconites lepisma, a bad term, for which it is better to say discus cyathiformis. In flowers with an ovarium inferum (Plate 5. fig. 9. c. 7. c) the discus necessarily ceases to be hypogynous, and generally also to appear in the form of scales. In Compositæ it is a fleshy solid body, interposed between the top of the ovarium and the base of the style; and has given rise, when much enlarged, to the unfounded belief in the existence of an ovarium superum in that order, as in Tarchonanthus. In Umbelliferæ it is dilated and covers the whole summit of the ovarium, adhering firmly to the base of the styles; by Hoffman it is then called stylopodium, a word which is seldom used.

Besides these forms of discus there is still another, called the gynobasis, a term which is used when the discus is enlarged, and as it were inserted under the ovarium to which it forms a sort of receptacle (Plate V. fig. 3.a). It occurs in Labiatæ, and Boragineæ, and especially in Ochnacea; and in many other orders. It ought, perhaps, to be considered a combination of the discus and receptacle.

It is an opinion that daily gains ground, that the discus is really only a rudimentary state of the stamens; and it is thought that proofs of the correctness of this hypothesis are to be found in the frequent separation of the cyathiform disk into bodies alternating with the true stamens, as in Gesneria; in its resemblance in Parnassia to bundles of polyadelphous

stamens, and particularly in the fact noticed by Mr. Brown, that an anther is occasionally produced upon the highly developed disk of Pæonia Moutan. To which may be added. the observation of Dunal, that half the disk of Cistus vaginatus occasionally turns into stamens. (Considerations, &c. p. 44.)

Like the petals, sepals, and stamens, the disk always originates from below the pistillum; but it often contracts an adhesion with the sides of the calyx, when it becomes perigynous, as in Amygdalus; or with both the calyx and the sides of an inferior ovarium, when it becomes epigynous, as in umbelliferous plants.

10. Of the Pistillum.

The last organ to enumerate in the flower is that which constitutes the female system, or gynææceum of Röper, and which is usually called the pistillum. In all cases it occupies the centre of the flower, terminating the axis of growth of the peduncle; and is consequently the part around which every other organ without exception is arranged.

It is distinguished into three parts; viz. the ovarium (Plate V. fig. 7. a), the style (fig. 7.f), and the stigma (fig. 7. g).

The ovarium, called germen by Linnæus, is a hollow case placed at the base of the pistillum, enclosing the ovula, and often containing two or more cells or cavities. It is the part which ultimately becomes the fruit; and consequently, whatever may be the structure of the ovarium such must neces sarily be that of the fruit; allowance being made, as will hereafter be explained, for changes that may occur during the progress of the ovarium to maturity.

Notwithstanding what has been stated of the pistillum constantly occupying the centre of the flower, and being the part around which all the other parts are arranged, an apparent exception exists in those flowers, the calyx of which is said to be superior (Plate V. fig. 7. & 9.), as the Apple blossom. In this instance the ovarium seems to originate below the calyx, corolla, and male system; on which account it is said to be inferior in such cases, while in the opposite state it is called

superior. But in reality, the inferior ovarium is only so in consequence of the tube of the calyx contracting an adhesion with its sides; and such being the case, the exactness of the description of the constant place of the pistillum as above, is unshaken. This is proved in many ways. In Saxifragem, the genus Leiogyne has the ovarium superior; in Saxifraga itself the calyx partially adheres to the sides of the ovarium, which then becomes half inferior, while in Chrysosplenium the union between the calyx and ovarium is complete, and the lattter is wholly inferior. Again, in Pomaceæ, the ovaria partially cohere with the calyx in Photinia, completely in Pyrus, and by their backs only in Cotoneaster; whence the ovarium is half superior in the first instance, quite inferior in the second, and what is called parietal in the third. Botanists call any thing parietal which arises from the inner lining or wall of an organ; thus in Cotoneaster the ovaria are parietal, because they adhere to the inner lining of the calyx, and in Papaver the placentæ are parietal, because they originate in the inner lining of the fruit.

Sometimes the ovarium, instead of being sessile, as is usually the case, is seated upon a long stalk; as in the Passion flower and the genus Cleome. This stalk is often called the thecaphore or gynophore; but it is obviously analogous to the petiole of a leaf, as will hereafter be seen, and the application of a special term to it appears unnecessary. M. Cassini calls the elongated apex of the ovarium of some Compositæ le plateau.

That part of the ovarium from which the ovula arise is called the placenta (Trophospermium, Richard; Spermaphorum, Colum, Receptacle of the Seeds). It generally occupies the whole or a portion of one angle of each cell (Plate V. fig. 1. e, 2. c, &c.), and will be spoken of more particularly hereafter. It is sometimes elongated in the form of a little cord, as in the Hazel nut, and many Cruciferæ such a part is called the umbilical cord (funiculus umbilicalis, podospermium).

:

The swelling of the ovarium after fertilisation is termed grossification.

The style (tuba of old authors) is that elongation of the ovarium which supports the stigma (Plate V. fig. 7.f). It is