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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    immediately dissolved on entering the circulation, though the spiral vessels contain an aeriform substance. The salts, we need not mention farther than to say that their inorganic ingredients are gathered from the soil by the water that saturates it, and by the water taken into the roots. Nitrogen is taken as ammonia and nitric acid. The first is formed abundantly by the decomposition of animal and vegetable substances, and forms a very small part of the atmosphere, from which it is thrown down by the rains and conveyed to the roots of plants. The second is produced during thunderstorms by the passage of electric sparks through watery vapors, also dissolved in water and thus absorbed. But salts, hydrogen, carbon, nitrogen, and oxygen, are far from being vegetable structures, though they are certainly the elements out of which veget- ables are formed. We cannot, perhaps, get a clearer insight into changes that occur dur- ing their organization than by observing the changes that occur in the plant during its fatal life, or while it is dependent on the materials stored up in the seed for its nourishment, and upon which it lives ex- clusively for a time after it begins that action which is to result in the formation of an independent organization. In the seed we have the germ; besides this, starch, fat, sugar, and an albuminous or nitrogenizedTsubstance, each bearing a proper relation to the other, and each refusing to be the first to make a move for life; and thus they may remain for centuries if no agent outside of themselves be brought to its aid. The seed is a combination of materials, a storehouse of valuable matter; but if locked up and unused will never change the relation of its own parts or its relation with surrounding objects; but give it water, and let a proper temperature be maintained, and import- ant changes soon occur. Without heat no change can take place in its nitrogenous elements; and without water, when the atoms would move one from the other, or one towards another, to effect new combinations, they could not take a single step in the direction desired; and without motion, no organization could occur, nor could it be maintained did it already exist. The nitrogenized element, under the stimulus of heat and by the aid of water, begins a movement in the atoms of starch; presently the atom of starch forms a strong attachment for two atoms of water, a union is then effected, the starch becomes a bigamist, and sugar is formed. At this stage of development sunlight is not important; for ger- mination proceeds rapidly in the dark so long as nutrient materials stored in the seed, starch, gum, sugar, and the like, furnish the materials for nourishing the forming tissues of the plant; indeed the air itself receives more from the embryonic plant than it furnishes to it; for if the seed be carefully weighed before germination, and the plant produced from it be carefully dried and weighed, it will be found that the plant actually weighs less than the seed from which it sprung. The carbonic acid given off during germination weighs more than the oxygen absorbed by it. A very different state of things exists in the plant after it is weaned. I say weaned, for, when the stock of food stored up with the germ is ex- hausted, the plant is forced to gather from the soil in which its roots are imbedded, or from the air in which its leaves are bathed, the support which it obtained from the original stock formed and stored up for use by the parent plant. The process of growth, while the seed furnishes the materials for the plant, goes on more favorably if pure water be fur- nished it than if the water contains carbonic acid; but the. reverse is true of an adult plant. Again, during the rapid growth of plants in the summer, the carbonic acid of the atmosphere is more rapidly taken ux> from the air than it is furnished to it by the various cotubustive processes that occur on the earth, and by the respiratory functions of animals; but during the winter the reverse is the case, for the animals exhale a larger amount of carbonic acid, fires burn more brightly and furnish large quantities to the air, whilst plants, during this cold period, absorb no carbonic acids at all from the air. Thus by opposing changes, effect- ed in the air by vegetables and animals, it is maintained in a nearly uniform condition, varying slightly with the season; but the excess of carbonic acid formed in winter by the combustive and respiratory changes is checked in summer, and consumed by vegetable nutritive changes
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