139

138. Legumen. 141. Conceptaculum, or 143. Capsule of Lychnis.

137. Apocarpous Capsule of Nigella. 139. Legumen with the two valves opened. 140. Folliculus. Double Folliculus. 142. Apocarpous Capsule of Delphinium. 144. Capsule of Lychnis cut through, and showing the free central placenta.

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

156, Cremocarpium of

154. Pyxidium of Anagallis.

159. Siliqua of Cruciferæ cut across.

Apiaceae cut across. 157. Siliqua of Cruciferæ. 158. Siliqua of Crucifera with the valves separating. 160. Cremocarpium of Apiacea. 161. Cremocarpium of Apiacea with the halves separating from their axis. 163. Etærio of Rubus. 164. Etærio of Boraginaceæ.

162. Bacca.

their ovules; and the two-celled ovary of some Pedaliacea 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

the seed, the latter being contained within the former. When the ovary is inferior, or coheres with the calyx, the latter and the pericarp are usually so completely united as to be inseparable and undistinguishable: in such cases it is usual to speak of the pericarp without reference to the calyx, as if no

such union had taken place. Botanists call a fruit, the pericarp of which adheres to the calyx, an inferior fruit (fructus inferus); and that which does not adhere to the calyx, a superior fruit (fructus superus). But Desvaux has coined other words to express these ideas: a superior fruit he calls autocarpien; an inferior fruit, heterocarpien; terms unnecessary and unworthy of adoption.

Every thing which in a ripe fruit is on the outside of the real integuments of the seed, except the aril, belongs to the pericarp. It consists of three different parts, the epicarp, the sarcocarp, and the endocarp; terms contrived by Richard, and useful in practice.

The epicarp is the external integument or skin; the endocarp, called putamen by Gærtner, the inner coat or shell; and the sarcocarp, the intermediate flesh. Thus, in the peach, the separable skin is the epicarp, the pulpy flesh the sarcocarp, and the stone the endocarp or putamen. In the apple and pear the epicarp is formed by the cuticle of the calyx, and the sarcocarp is confluent with the remainder of the calyx in one fleshy body.

The pericarp is extremely diversified in size and texture, varying from the dimension of a single line in length to the magnitude of two feet in diameter; and from the texture of a delicate membrane to the coarse fabric of wood itself, through various cartilaginous, coriaceous, bony, spongy, succulent, or fibrous gradations.

The base of the pericarp is the part where it unites with the peduncle; its apex is where the style was: hence the organic and apparent apices of the fruit are often very different, especially in such as have the style growing from their sides, as in Rosacea and Chrysobalanaceæ, Labiatæ and Boraginaceæ.

When a fruit has arrived at maturity, its pericarp either continues perfectly closed, when it is indehiscent, as in the

hazel nut; or separates regularly round its axis, either wholly or partially, into several pieces: the separation is called dehiscence, and such pieces valves; and the axis from which the valves separate, in those cases where there is a distinct axis, is called the columella.

When the dehiscence takes place through the dissepiments, it is said to be septicidal; when through the back of the cells, it is called loculicidal; if along the inner edge of a simple fruit it is called sutural; if the dissepiments are separated from the valves, the dehiscence is named septifragal.

In septicidal dehiscence the dissepiments divide into two plates and form the sides of each valve, as in Rhododendron, Menziesia, &c. Formerly botanists said that in this sort of dehiscence the valves were alternate with the dissepiments, or that the valves had their margins turned inwards.

This may

169

d

d

a

v

be understood from fig. 169., which represents the relative position of parts in a transverse section of a fruit with septicidal dehiscence; v being the valves, d the dissepiments, and a the axis.

In loculicidal dehiscence the dissepiments form the middle of each valve, as in the lilac, or in the diagram 170., where the letters have the same value as above. In this it was formerly said that the dissepiments were opposite the valves.

In septifragal dehiscence the dissepiments adhere to the axis and separate from the valves, as in Convolvulus; or in the diagram 171., lettered as before.

In sutural dehiscence there are no dissepiments, the fruit being composed of only one carpel, as the Pea.

d

a

ย

d

170

171

Besides these regular forms of valvular dehiscence, there is a mode which obtains in a very few plants, called circumscissile. This occurs by a transverse circular separation, as in Anagallis; in Jeffersonia it only takes place half round the fruit.

Q

Valvular dehiscence, which is by far the most common mode by which pericarps open, must not be confounded with either rupturing or solubility, -irregular and unusual contrivances of nature for facilitating the dispersion of seeds. In valvular dehiscence the openings have a certain reference to the cells, as has been already shown; but neither rupturing nor solubility bear any distinct relation to the cells. Rupturing consists in a spontaneous contraction of a portion of the pericarp, by which its texture is broken through, and holes formed, as in Antirrhinum and Campanula. Solubility arises from the presence of certain transverse contractions of a one-celled pericarp, through which it finally separates into several closed portions, as in Ornithopus.

For the nature of the placenta and umbilical cord see the observations under ovary. These parts, which are mere modifications of each other, essentially appertain to the pericarp, in which the former often acquires a spongy dilated substance, occasionally dividing the cells by spurious dissepiments, and often giving to the fruit an appearance much at variance with its true nature. In some seeds, as Euonymus europæus, it becomes exceedingly dilated around each seed, forming an additional envelope, called aril. The true character of this organ was unknown till it was settled by Richard: before his time the term was applied, not only in its true sense to an enlargement of the placenta, but also to the endocarp of certain Rubiacea and Rutaceæ, to the seed-coat of Jasminum, Orchidea, and others, and even to the perianth of Carex. A very remarkable instance of the aril is to be found in the nutmeg, in which it forms the part called the mace surrounding the seed. It is never developed until after the fertilisation of the ovule.

Having thus explained the structure of the pericarp, it is in the next place necessary to enquire into the nature of its modifications, which in systematic botany are of considerable importance. It is, on the one hand, very much to be regretted that the terms employed in this department of the science, which is that of Carpology, have been often used so vaguely as to have no exact meaning; while, on the other hand, they have been so exceedingly multiplied by various writers, that