« PreviousContinue »
are powerfully odorous, slightly soluble in water, with which they pass over in distillation, communicating their flavor to it; and that they are volatilized by heat without decomposition. The fixed oils, on the contrary, are inodorous and insipid, support two or three hundred degrees of heat without volatilizing, and are decomposed at a higher temperature. In a physiological point of view their difference is equally striking. The volatile oils are found in the leaves or in the cortical system, the usual place of the secretions; the fixed oils are either situated in the seeds themselves, or more rarely in the tissue of the pericarp. 52. There are many local secretions, of which a detailed account belongs more properly to a chemical treatise than to one that, like the present, is only . physiological, and also too brief to do more than glance at the other sciences immediately connected with the subject: it will therefore only be possible to notice these secretions slightly here. They consist of acids, such as citric, malic, acetic, &c., prussic acid (remarkable by the absence of oxygen) which is found in peach and laurel leaves, &c., of Gluten, Albumen, Tannin and Coloring matter, of which indigo is one of the most important, and a variety of other secretions or principles, each confined to the particular vegetable in which it is found, such as Asparagin, whose name denotes its origin from the asparagus. 53. Besides the above, substances are found in plants which are purely mineral, and which are principally lime, magnesia, silica, alumina, and perhaps barytes. Potash and soda are found in very large quantities. Iron, manganese, and copper" have
* Copper was found by M. Bischoff, Dr. Meissner and M. Sarzeau. See De Candolle, Phys. Veg., vol. i. p. 389. . .
been observed, and besides the above there are occasionally found in plants chlorine, iodine, sulphur, and phosphorus. The reader is referred to No. 4 of these little treatises" for further particulars on the chemical part of the subject.
54. Those whose leisure permits, and whose inclination leads them closely to examine into the simple yet marvelous chemistry by which compounds, absolutely essential to the animal economy, but which it has no direct power of preparing for itself, are formed for it in the vegetable organism, will perceive how true it is that the more we search into those phenomena which we daily and hourly witness and experience, the more we shall see that nothing has been made in vain, and the more resistless will be the proof that such a chain of causes and effects as may be traced from one end of creation to the other, could only have had their origin in that One Mind to which everything is ever present, and who, in the very “constitution and course of nature,” has stamped too deeply to be effaced, even amid the moral disorder man’s folly has introduced, the “image” of his own perfection, and the “superscription” that the work of his hand is “very good.” To God then let all “render the things that are God's,” by a full acknowledgment of his wisdom and goodness in thus supplying what they need, and by making such a use of those gifts as may best prove their gratitude, and most tend to the glory of the Giver.
* “Introduction to Organic Chemistry.”
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 aestivation. 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.t 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.”
t If but one whorl exists it is always considered by botanists as a Calyar, 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. 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.”f The shape of the pollen grains varies extremely; “its function is to vivify the ovules.”f 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 22) and in another in the same language (“Ueber das Pollen der Asclepiadeen”) by Ehrenberg.
t Lindley, El. Bot., pp. 47, 49, 50. f Ibid.