CHAPTER IV.

REPRODUCTION OF PLANTS.

55. The reproduction of plants from seed is the chief object of all those wonderful organs, a description of which will now be given, and it would be difficult if not impossible to find in the whole of the beautiful world around us, anything more admirable than the organization by which that object is attained; while the parts are, in many instances, so minute as to require the assistance of the microscope to discover them at all. It has been said above, that the chief office of that lovely portion of the vegetable kingdom, the flowers which glow like gems in our sight, is to reproduce the species; but it would be ingratitude to assert that they have no other end to answer. The mere purpose of reproduction might doubtless have been effected with no beauty to charm the eye, but it pleased Him who made that exquisite organ, also to furnish it with objects that should delight it, and we can scarcely behold these jewels of the field, and not say of them as the son of Sirach did of the brilliant bow whose tints they emulate, "Look on the flowers' and praise Him who made them; very beautiful they are in the brightness thereof."

56. Plants are distinguished, with reference to the organs of fructification, into two great classes,— phanerogamic, or those which have their flowers visible to the naked eye, and are more or less symmetrical; and cryptogamic, in which the flowers, if they exist, are invisible except by the microscope,

and are little, if at all, symmetrical. In the former group the seed-bearing and fecundating organs are very distinct; in the latter they are not so.-The first include all the Exogenes, and the greater part of the Endogenes; the second all the cellulares, and some of the Endogenes.

57. At a longer or shorter period before a Phanerogamic plant is about to put forth blossoms, points appear called Flower Buds, surrounded like the Leaf Buds above described, by developed or undeveloped leaves, and like them really situated at the axil of a leaf, though that leaf may have been rudimentary and obliterated,*-these points in due time expand into the perfect flower-and if a transverse section be made of them, they will be found to be most exquisitely folded together in the state to which botanists have applied the term æstivation.

When the Flower Buds are unfolded and have expanded into flowers, they are seen to be composed of one or more whorls of leaves, surrounding and protecting the organs of reproduction.† In anatomical structure they do not differ from true leaves.

* The subject of symmetrical arrangement in the parts of a plant is a very curious one, but involves too much technical and botanical detail to be properly introduced here. Whether it really exist to the extent that botanists have supposed, or not, there is ample proof that the general law is that of symmetry, and the deviations from it the exceptions: the reader who wishes for detailed information on this point is referred to the 6th chapter ("Morphology") of Professor Henslow, "Principles of Descriptive and Physiological Botany."

+ If but one whorl exists it is always considered by botanists as a Calyx, whether it be green or colored,-if more than one whorl is present the outer one is always the calyx, the inner whorls being the Corolla,-while the general term Perianth, is applied to the whole floral envelop together, any more minute notice of the forms and divisions of the calyx and corolla would be inconsistent with the intention of the present treatise, which does not profess to be an Introduction to Botany.

Situated immediately within the inner whorls of these leaves, if more than one be present, we find the organs of fructification, the Stamens and Pistils.

58. Each Stamen consists of two parts, the anther, and the filament; the latter is a slender stalk by which the stamen is attached to the flower, but is not an essential portion of the organ, and is sometimes wanting; it is formed of spiral vessels, surrounded by cellular tissue-on the top of this filament, or occasionally, though rarely, sessile on the flower, is the Anther, a case of cellular tissue, usually consisting of two lobes, which contain the Pollen. This is the indispensable part of the fructifying organ.

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59. The Pollen* is a collection of minute cases, containing a fluid in which float grains of starch and drops of oil. It is furnished with apertures through which its lining is protruded, in the form of a delicate tube, when the pollen comes in contact with the stigma." The shape of the pollen grains varies extremely; "its function is to vivify the ovules."+

60. The Pistil occupies the centre of the flower, and consists of three parts; the ovary, the style, and the stigma. "The ovary is a hollow case enclosing ovules (or young seeds). It contains one or more cavities, called cells. The stigma is the upper extremity of the pistil. The style is the part that connects the ovary and stigma; it is frequently absent, and is no more essential to a pistil, than a

* Any one who wishes to study minutely the wonderful varieties in form, &c., of the Pollen will find the subject illustrated by most exquisite microscopic drawings in the German work by Fritzsche (Ueber den Pollen ") and in another in the same language (Ueber das Pollen der Asclepiadeen") by Ehrenberg. Lindley, El. Bot., pp. 47, 49, 50.

+ Ibid.

The

petiole to a leaf, or a filament to an anther."* pistil, or ovarium, is frequently composed of several carpels, (61) each having its separate ovary, style, and stigma.

61. Carpel. The pistil, anatomically considered, is in reality a modified leaf, or whorl of leaves, and a carpel "is formed by a folded leaf, the upper surface of which is turned inwards and the lower outwards; and within which are developed one or a greater number of buds, which are the ovules."t

62. The Ovule, as has just been seen, is contained within the carpel, and becomes the germ of the new plant; it is either naked or enclosed in a covering, sometimes sessile, sometimes stalked in its most complete state it consists of a nucleus, surrounded by two coats or integuments.

63. The Fruit is the mature state of the pistil or carpels.

* Lindley, El. Bot. pp. 47, 49, 50.

+ Lindley's Elements of Botany, p. 50.

Professor Lindley has made the subject of the carpels so clear in his "Ladies' Botany" that it may be well to add his explanation to what is given above. "Next to the stamens, and oce cupying the very centre of the flower," (the common Ranunculus, or Buttercup, is the one he takes as his example,)" are a number of little green grains, which look almost like green scales; they are collected in a heap, and are seated upon a small elevated receptacle; we call them carpels. They are too small to be seen readily without a magnifying glass; but if they are examined in that way, you will remark that each is roundish at the bottom, and gradually contracted into a kind of short bent horn at the top; the rounded part is the ovary, the horn is the style; and the tip of the style, which is rather more shining and somewhat wider than the style itself, is named the stigma: so that a carpel consists of ovary, style, and stigma. At first sight you may take the carpels to be solid, and, if you already know something of botany, you may fancy them to be young seeds; but in both opinions, you would be mistaken. The ovary of each carpel is hollow and contains a young seed called an ovule, or little egg; so that the carpel, instead of being the seed, is the part that contains the seed." (Letter I. p. 7.)

64. The ovary of the pistil becomes what botanists call the Pericarp of the fruit; it has a great variety of names, dependent on the number of carpels, their situation, the quality of their texture, &c.

65. The Seed is the perfected ovule; it is covered with an integument, which is sometimes curiously spread out so as to form wings, and contains the embryo lying in it as the embryo chick is in the egg, and often similarly surrounded by the albumen which affords its nourishment.

66. Spores. The principal organs of reproduction in those plants, called Acrogens or Flowerless, which are destitute of stamens and pistils, are called spores; these are cells which are seen by a microscope to be analogous to a grain of pollen; the cases containing them are termed thecæ or sporangia.

Sori are clusters of thecæ, and the Indusium is a portion of the epidermis which encloses them.

67. The reproduction of plants is of two kinds, that by seed and that by division, which is either natural or artificial, and will afterwards be noticed. When the flower is fully developed,-a period which arrives in different kinds of plants at very different times,—in some for instance, in the first, in others in the second year of their existence, a process occurs by which that contact between the pollen (59) and the stigma (60) takes place, which in all the phanerogamic plants is absolutely essential to the reproduction of the species by seed. This contact or impregnation is thus effected. "The pollen emits a tube of extreme delicacy, which pierces the stigma and style, and passing downwards into the ovary,' "* thus reaches the ovule. The result of this process is the gradual development of the embryo

* Lindley's "Elements of Botany,” p. 56.