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clearly understood what he saw, and that the best account of the ovule is given by Fritzsche in Wiegmann's Archiv. : that, in many plants, the ovule has but one integument, as in Coniferæ, Compositæ, Lobeliaceæ, Gentianaceæ, &c.; and in others two, as in Polygonaceæ, Cistaceæ, Urticaceæ, Araceæ, and all other endogens, &c. He also appears to deny the existence of a tercine, as he expressly does that of a quartine; and I do not clearly understand whether he regards the quintine as belonging to the pollen tube, or as being the sac of the amnios, as it surely is. He moreover finds that while all endogens have two integuments of the ovule, the majority of monopetalous exogens have but one, whilst the polypetalous usually possess two.
Schleiden states that “the plan which nature adopts is simply this :— The example I shall select is that of the atropous ovule, for instance of the Polygonaceæ, as being the most simple. At a certain distance below the apex of the original protuberance an ideal line may be recognised, intended as the basis of the nucleus, which does not afterwards increase in thickness. Above this line the apex forms itself into the nucleus, and below it the substance of the axis expands and forms a protuberance, which extending itself as a kind of membranous fold gradually covers in the nucleus (Integumentum primum aut internum, mihi; Secundine, Mirb.; Membrana interna, Auct.). Sometimes soon after, and indeed almost contemporaneously with this, sometimes later, sometimes immediately below the first protuberance, at other times at some distance from it (as, for instance, in many Polygonaceæ and Cistaceæ), we may next observe a second protuberance, which, as the second integument, covers in the first (Integumentum secundum sive externum, mihi; Primine, Mirb.; Testa, Auct.). The first-formed integument certainly does frequently consist only of a fold of the epidermis of the nucleus ; nevertheless, we find a tolerably thick parenchyma taking part in its formation in almost all those families which form no second integument, and also in some which possess both coverings, as, for instance, in the Euphorbiaceæ, Cistaceæ, and Thymelaceæ. In the case of these three families, a peculiar process takes place; namely, upon the seed becoming ripe the external integument is gradually absorbed, until nothing but a thin membrane is left, usually described as epidermis testæ, or in the Euphorbiaceæ it has been given as arillus; and, on the other hand, the actual modified epidermis testæ has also been described as the arillus, for instance, in the Oxalideæ.
The apex of the original papilla, which developes itself as nucleus, varies exceedingly in its size in proportion to the entire ovule, if examined in the different families. It often forms a long and nearly cylindrical body, as in Loasa and Pedicularis; in many cases it is shorter, so that that portion of the ovule in which no distinction has taken place between nucleus and integument (the whole being like a feshy distended stalk) is by far the more predominant, as in all the Synanthereæ, Canna, Phlox, Polemonium : it consists, again, in some instances merely of the extreme point of the papilla itself, as in Convolvulus; or nothing more than an ideal point remains, which can no longer be distinguished as an independent body, above which, however, a protuberance developes itself, and thus forms a micropyle, as in the Dipsaceæ. Of course the process I have been describing becomes considerably modified in individual points.”
Although the structure of the ovule is in general such as is above described, yet there is an exception to it of a character too remarkable to be passed over in silence. According to Mr. Griffith, the ovulum of Santalum album consists of nothing more than a naked nucleus, from within the apex of which the sac of the amnios protrudes in the form of a long tubular process. The same excellent botanist states that Loranthus and Viscum have an equally simple ovulum, and he considers it probable that it will hereafter appear that the sac of the amnios is the only essential part of an ovule. (Linn. Trans. xviii. 77.)
The fluid matter contained within the nucleus is called the liquor amnios, and is supposed to be what nourishes the embryo during its growth.
When an ovule grows erect from the base of the ovary, it is called erect; when from a little above the base, ascending ; when it hangs from the summit of the cavity, it is pendulous ; and when from a little below the summit, it is suspended.
14. Of the Fruit.
The fruit (figs. 136. to 168.) is the ovary or pistil arrived at maturity; but, although this is the sense in which the term is strictly applied, yet in practice it is extended to whatever is combined with the ovary when ripe. Thus the pine-apple fruit consists of a mass of bracts, calyxes, corollas, and ovaries; that of the nut, the acorn, and many others, of the superior dry calyx and ovary; that of the apple of a succulent superior calyx, corolla, and ovary; and that of the strawberryblite of a succulent inferior calyx and dry ovary.
The fruit being the matured ovary, it should exhibit upon some part of its surface the traces of a style or stigma; and this mark will, in many cases, enable the student to distinguish minute fruits from seeds. Many fruits were formerly called naked seeds, such as those of Apiaceæ, Labiatæ, and Boraginaceæ, and the grain of corn; but, now that attention has been paid to the gradual developement of organs, such errors have been corrected. In cases where a trace of the style cannot be discovered, anatomy will generally show whether a minute body is a seed or fruit, by the presence, in the latter case, of two separable and obviously organically distinct coatings to the nucleus of the seed; but in other cases, where the pericarp and the integuments of the seeds are combined in a single covering, and where no trace of style remains, as sometimes happens, nothing can be determined as to the exact nature of a given body without following it back in its growth to its young state. This, however, may be stated, that naked seeds, properly so called, are not known to exist in more than three or four orders in the whole
vegetable kingdom ; viz. in Coniferæ and Cycadaceæ, where the ovules also are naked, and in Peliosanthes Teta and Leontice, in which the ovules, originally enclosed in an ovary, rupture it at an early period after fertilisation, and subsequently continue naked until they become seeds.
Such being the case, it follows that all the laws of structure which exist in the ovary are equally to be expected in the fruit; and this fact renders a repetition in this place of the general laws of formation unnecessary. Nevertheless, as, in
141 143 144
139 136 Syncarpous Capsule of Euonymus. 137. Apocarpous Capsule of Nigella. 138. Legumen.
139. Legumen with the two valves opened. 140. Folliculus. 141. Conceptaculum, or Double Folliculus. 142. Apocarpous Capsule of Delphinium 143. Capsule of Lychnis. 144. Capsule of Lychnis cut through, and showing the free central placenta.
159 145. Samara. 146. Capsule of Rhododendron. 147. Capsule of Rhododendron divided across
148. Capsule of Staphylea. 149, 150. Cypsela of Compositæ. 151. Capsule of Aristolochia. 152. Capsule of Aristolochia cut across. 153. Capsule of Staphylea cut across.
the course of the advance of the ovary to maturity, many changes often occur which contribute to conceal the real structure of the fruit, it is in all cases advisable, and in many absolutely necessary, to examine the ovary, in order to be certain of the exact construction of the fruit itself. These changes are caused by the abortion, non-developement, obliteration, addition, or union of parts. Thus the three-celled six-ovuled ovary of the oak and the hazel becomes, by the non-developement of two cells and five ovules, a fruit with one seed; the three-celled ovary of the cocoa-nut is converted into a one-celled fruit, by the obliteration of two cells and
161 158 157 154. Pyxidium of Anagallis. 155. Cremocarpium of Apiaceæ. 156, Cremocarpium of
Apiaceæ cut across. 157. Siliqua of Cruciferæ. 158. Siliqua of Cruciferæ with the valves separating. 159. Siliqua of Cruciferæ cut across. 160. Cremocarpium of Apiaceæ. 161. Cremocarpium of A piaceæ with the halves separating from their axis. 162. Bacca. 163. Etærio of Rubus. 164. Etærio of Boraginaceæ.
their ovules; and the two-celled ovary of some Pedaliaceae becomes many-celled, by a division and elongation of the placentæ. In Cathartocarpus Fistula a one-celled ovary changes into a fruit having each of its many seeds lodged in a separate cell, in consequence of the formation of numerous horizontal membranes which intercept the seeds. A still more extraordinary confusion of parts takes place in the fruit of the pomegranate after the ovary is fertilised; and many other cases might be mentioned.
Every fruit consists of two principal parts, the pericarp and