Vegetable physiology : an address before the Missouri State Horticultural Society, January, 1864 / by Prof. John T. Hodgen.

  • John T. Hodgen
Date:
[1864]
Catalogue details

Licence: Public Domain Mark

Credit: Vegetable physiology : an address before the Missouri State Horticultural Society, January, 1864 / by Prof. John T. Hodgen. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    \: 6 during the Summer, so that the rain, falling daring early summer, when mng plants have set up an Independent life, holds a Larger pro- portion of carbonic acid in solution than at any other time; and this material is of ^reat importance to the growth of plants, since carbon forms a large part of all their structures. But carbon is not alone supplied by the water absorbed by the roots of plants; as the leaves and other parts absorb carbonic acid, and give off oxygen in the presence of sunlight. That sunlight is the agent that forces tlus act is shown by the fact, that during the night the carbonic acid absorbed in solution of water by the roots, is given oil' by the leaves and other parts of plants. Again, plants grown m darkness do not ac- cumulate carbon, and only gain in weight by holding a larger proportion of water than entered into the formation of the seeds from which they gre w. The green parts of plants, it has been taught, were the only pacts that have the power of nxiug carbon in the tissues; but that this power is not due to the green parts, is shown by exposing a perfectly white newly grown stalk to the light, when it immediately begins its function of fix- ing carbon, and soon assumes, as a consequence, a green color; and, although the green parts of plants are the most active agents in fixing carbon, aided by the force of sunlight, it is due rather to the fact (hat here the sap or blood of plants comes more nearly in contact with the atmosphere and is more exposed to light than in other parts ooverad with a thick bark, where the sap vessels are not so abundant nor in so ax* osed positions. The great object of vegetable organization seems to e to combine inorganic materials to form an organization that Is to take certain salts of lime, magnesia, potash, soda, and the like, with oxygen, hydrogen, nitrogen and carbon, and blend them one with the other and form an organized structure. JJow there is no possible combination of these elements that can form a tree or slirub, or indeed a single cell, simply because these elements are not all that enter into the formation of a cell, a plant, or an animal, even physically considered, but, as we have seen, light is essential to the growth of a plant after it has exhausted the limited supply stored in the seed from which it springs. 11 rat, too, seems to exercise an important influence; for in plants grown under a vertical sun, or at that day, thickly obscured by the unnumbered years of the past, when the earth's internal heat was so great that the di- rect rays of a midsummer's sun, or the oblique glancing* of his winter rays neither hastened nor retarded the growth of those plants that now form the deeper strata of our coal bids, marking them not with annual rings, by which we might determine the years required for their growth, but leav- ing them as silent records of the unvarying temperature in which they grew ; while in regions farther removed, both in time and space, from an unvarying temperature, trees have each year of their existence recorded in their structures. Again, both heat and light are lost, or to use a more favorite expres- sion, are rendered latent in the growth of plants, and made sensible again by their decomposition or the return of their elements to their ori- ginal condition as inorganic matter; and this is equally true, though not equally apparent, whether they return rapidly by active combustion, or slowly by eremacausis. Thus, then, as from the structures of plants, by decomposition, is given back to the inorganic world the materials that were drawn from it for their formation, so too the imponderable agents or forces, light, heat, and electricity, are restored to the universe at large;. So, if a certain amount of inorganic material is drawn from the earth and air, and a certain amount of force is borrowed from the sun for the development of plants, not only do we see the inorganic materials re- turned in the precise form in which they came, but the imponderable also are returned; not only so, but the carbonic acid, nitrogen and oxygen and hydrogen are restored to the air and water, and the saline materials are (jivon back to the earth. Thus nothing is lost, nothing is gained, nothing is changed, except in point of form; and though carbon and hydrogen, with light and heat, may have been stored up in coal beds for millions of years, men are now searching the very bowels of the earth and restoring to the inorganic world its original matter in its original form. But vegetable matters do not always return to th( ir inorganic state without still further modification; for all the auimals of the earth
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