Colin Ingerfurth Beginner
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Posts by Colin Ingerfurth

    The amount of sugar made, carbon dioxide taken in, and oxygen given off by this process suggests that while leaves may be very tiny factories they are among the most efficient in the world. Assuming an area of leaf surface equal to about a square yard the amount of sugar made would be about one-third of an ounce in a day or nearly three pounds in a single growing season. Carbon dioxide withdrawn from the air would average from the same area of leaf surface about two gallons a day or over three hundred gallons for the season. As an equal amount of oxygen is given off by the leaf, it becomes clear that as all of this interchange must go through the stoma the functioning of these and their guardians must be nearly one hundred per cent perfect. As we shall see a little later, they perform still other duties with even greater perfection. When we stop to reflect what an absurdly minute fraction one square yard of leaf surface is to the total leaf surface in the world, we come to some realization of the gigantic proportions of this process of manufacturing sugar and exchange of gases mutually useful to animals and plants. While in the United States most of the leaves fall in the autumn, the great bulk of the vegetation of the world holds the greater part of its leaves all the year, notably in the vast evergreen forests in the north, and of course practically all tropical vegetation. Chlorophyll in such places works continually and what the total of sugar production may be no man can even guess.

    As a result of their various synthetic and metabolic activities, a great variety of organic compounds is produced by plants. Certain types of these compounds, such as the carbohydrates and proteins, are necessary to all plants and are elaborated by all species of autotrophic plants. Other types of compounds are produced by many, but not all, species of plants; while still others are found in only a few species. It is fairly easy to classify all of these compounds into a few, well-defined groups, based upon similarity of chemical composition. These groups are known, respectively, as the carbohydrates and their derivatives, the glucosides and tannins; the fats and waxes; the essential oils and resins; organic acids and their salts; the proteins; the vegetable bases and alkaloids; and the pigments. A consideration of these groups of compounds, as they are synthetized by plants, constitutes the major portion of the study of the chemistry of plant life as presented in this book. Following the discussion of the compounds themselves, the chapters dealing with enzymes, with the colloidal nature of protoplasm, and with the supposed accessory stimulating agencies, aim to show how the manufacturing machine known as the plant cell accomplishes its remarkable results, so far as the process is now understood.

    For purposes of study, these compounds may conveniently be divided into three groups; namely, the natural gums and pentosans, the pectins and mucilages, and the celluloses. The segregation into these three groups is not sharply defined. The distinction between the groups is based upon the solubility of the compounds in water. The gums and pentosans readily dissolve in water; the pectins form colloidal solutions which are easily converted into "jellies"; the mucilages do not dissolve but form slimy masses; while the celluloses are insoluble in and unaltered by water. Some authors add a fourth group, known as "humins"; but as these are the products of decay (usually in the soil) of these structural compounds, rather than of growth and development, they need not be taken into consideration in a study of the chemistry of plant growth.