it is capable of receiving the influence of temperature. It is, moreover, the medium by which the nutritious principles that are deposited in the earth are absorbed by the roots, and conveyed from one part of the system to another. "To sum up in a few words all that has thus far been stated, it is light, heat, and water, acting in concert upon the irritable membrane, which enable plants, by virtue of their extensibility, elasticity, and hygrometrical powers, to perform the phenomena of contraction and endosmose, by means of which they absorb and digest their food, circulate their fluids, develop their organs, increase in size, and reproduce themselves.* "Under the name of respiration, we shall include all that is connected with the inhaling and giving off of gaseous matter. This function is chiefly connected with the absorption of oxygen and carbonic acid, and their expiration. By a vast number of experiments chemists have determined that the green parts of plants placed in the sun absorb carbonic acid from the atmosphere, and decompose it, giving back the oxygen; and that at night they absorb oxygen from the atmosphere, giving off carbonic acid: it is also probable that they part with a small quantity of carbonic acid during the day. These conditions are necessary in order to secure the disengagement of oxygen by leaves: firstly, the parts must be green; secondly, they must be exposed to the direct action of the solar rays; and thirdly, there must be carbonic acid in the water. 66 It is not sufficient to place leaves in bright light to procure the emission of oxygen by their leaves in water; it must be under the direct rays of the sun. De Candolle found the purest daylight, the brightest lamplight, insufficient to produce the phenomenon; a very .curious result when we consider how large a part of vegetation is seldom exposed directly to the solar rays. From whence, it may be inquired, is the large quantity of carbonic acid obtained which is thus necessary to the support of plants? Certainly not from the atmosphere alone, for it does not usually contain one part in a thousand of carbonic acid. There can be no doubt that this gas is supplied principally by the Earth, in which it exists in great quantity; that a part is obtained from the atmosphere; and that a certain other portion results from the combination of the oxygen of the atmosphere with the carbon of vegetation; and it would seem as if a repeated decomposition and recomposition of carbonic acid was the principal phenomenon in respiration.t "What we have now seen of the action of the leaves and green parts of plants will enable us to appreciate the adaptation of their internal structure to perform their functions. We have found them to consist of a number of little cells or bladders, so loosely cohering that the air has room for free circulation between them; and that, by the way in which they are arranged, they present the greatest possible surface to the action of the atmosphere. Although they are enclosed in a thick cuticle, yet they are provided with openings through it, called stomates, by means of which free admission for air is secured, See 120th Theorem. + See 124th Theorem. and through which it may be expelled again with facility when they are submersed, and are, consequently, neither exposed to irregularities of temperature nor of dryness in the air. . . . . It is true that M. de Candolle entertains doubts whether the stomates are not rather organs of evaporation; but when we consider the relation they bear to the air-cavities in leaves we can scarcely doubt that they are really respiratory organs; nor does it appear clear why they should not, in fact, perform the functions both of perspiration and respiration. If we hold a leaf of Laurustinus over a candle, so as to heat the air contained in it without burning the leaf itself, the air will be expelled through the stomates with such force as to extinguish the flame." * These explanations of the phenomena attending the organization, the respiration, and the evaporation of perfect flowering plants, together with the manner in which they form and decompose carbonic acid, are amply sufficient to show that sun-light and atmospheric air are indispensably requisite for effecting those important functions of the vegetable economy; and, consequently, it is quite unnecessary to prove that none of the flowering plants requiring these essential elements could have existed previously to the formation of the light and of the atmosphere; and are, on that account, to be considered as not having, in any way whatever, contributed to those widely extended and important labours performed by the agency of plants during the protracted period of non-rotation. They may, I therefore apprehend, after a few further explanations, be eliminated altogether from the future argument. They did not then exist. water. But, to leave no lingering doubt unremoved, let it be next inquired whether they could have fulfilled the end of their being their reproduction--had they been submerged in I shall first recapitulate the hundred and eighteenth Theorem That all the phenomena attending the flowering of plants, and the dehiscence of the various receptacles which are instrumental in the fertilisation and maturation of the SEED and FRUIT, and the dissemination of the former, fully attest the absolute necessity of these COMPLICATED OPERATIONS BEING CONDUCTED IN ATMOSPHERIC AIR; the presence of much moisture being prejudicial to the peculiar development of the pollen;" and, in continuation, I shall give a few corrobora "Botany," in Library of Useful Knowledge, pp. 21, 28-31, 79, 80, 87–90. tive extracts, although the Theorem itself is almost sufficiently conclusive: : "It is further essential," says Professor Henslow, "that the pollen should be protected from the influence of moisture; and, consequently, we find that aquatics, as the water-lily (Nymphæa alba), elongate their flower stalks until the blossoms float upon the surface of the water. In the water-soldier (Stratiotes aloides), water-violet (Huttonia palustris), and others, the entire plants float to the surface of the water during the period of flowering, but live submerged at other times. In the Zostera marina the flowers are arranged within a cavity filled with air; and thus, although they are developed beneath the surface, they are protected from the immediate contact of the water. "The salt of sea-water produces an injurious effect upon the seeds of plants, and completely destroys the vitality of those which are long subjected to its influence." * "When the flower unfolds," observes the writer on Botany in the "Library of Useful Knowledge," "the anther is a tolerably solid, moist body, filled with moist pollen. The grains of the latter contain a fluid more dense than the tissue that forms a covering for them, and rapidly absorbs its moisture from the anther-case. As soon as this has happened to any great extent, the tissue of the anther-case contracts, and at first rends into grated cells of various forms; as the dryness is increased, these latter contract still further, and exercising a general power over the whole surface of the lining would, in the end, be rent into still finer portions, if it were not for the slight degree of cohesion which exists between the valves of the anther at the sutural line." + These quotations sufficiently prove that atmospheric air is not more essential to the entire phenomena connected with the development and reproduction of the Monocotyledonous and Dicotyledonous plants than that an undue degree of moisture is prejudicial to these functions: consequently, deprivation of the light and atmospheric air and submersion in water would have been altogether destructive of those important processes in flowering plants. They could not, in such a condition, have existed. But, on the other hand, as the most perfect wisdom pervades the whole design of Creation, it is but just to conclude that an adequate motive existed for the adoption of whatever principle may be evidently traceable in it. There is a principle peculiarly observable in the formation of the Vegetable Kingdom. The two great classes of plants which were called into existence * Botany, in Cab. Cyc., pp. 263, 266, 303. after the formation of the light, the atmosphere, and the "dry land," were flowering plants, whose submersion in water, as has just been made apparent, would have been wholly destructive of their propagation; while those which existed before were flowerless plants, possessing neither stamen, stigma, nor pollen, radical nor plumule; therefore it is allowable to conclude that light or atmospheric air was not indispensably essential, nor was water inimical to the maturation, or to the subsequent development and germination, of their reproductive organs, whether these were sporules, cones, or dot-like bodies. SECTION II. THE VEGETABLE ORGANISMS OF THE PERIOD OF NON-DIURNAL ROTATION. CHAPTER VI. THE important results which were come to at the conclusion of the preceding chapter will be greatly confirmed should it be found that what was deduced from reasoning d priori, agrees with that which experimental botanists declare to prevail amongst the interesting objects of the vegetable kingdom now under consideration; for, if those two branches agree, we can scarcely any longer entertain a doubt. According to the consolidated lists which have been given, the plants found in the stratified masses, which have been identified and classed, consist of 1. Algæ; 2. Filices; 3. Characeæ; 4. Lycopodiacea; 5. Marsileacea; 6. Equisetacea; 7. Naiades, or Fluviales; 8. Cycades; 9. Euphorbiaceæ, with a few Coniferæ and Palmæ, some Cannæ, and others still uncertain as to class and genera, which consequently cannot be taken into account. But to those which have been identified I shall affix, in the order in which they stand, a succinct account of their usual characteristics and habitats. "ACOTYLEDONS. "ORDER III. ALGE.-Vegetables, for the most part aquatics, destitute of roots, or furnished only with a fibrous or scutate base for the purpose of attachment merely; having, for fructification, seeds or sporules. "Many species of this singular and, generally speaking, beautiful |
