Samira Ullrich Beginner
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Posts by Samira Ullrich

    The many theories which have been advanced concerning the nature of the chemical changes which are involved in photosynthesis have served as the basis for much experimental study of the problem. The following brief summary will serve to point out the general trend of these investigations and the present state of knowledge concerning the chemistry of photosynthesis.

    Von Baeyer, in 1870, advanced the hypothesis that the first step in the process is the breaking down of carbon dioxide into carbon monoxide and oxygen and of water into hydrogen and oxygen; that the carbon monoxide and hydrogen then unite to produce formaldehyde, which is immediately polymerized to form a hexose.

    There is considerable experimental confirmation of the soundness of this view. The whole photosynthetic process takes place in chlorophyll-containing plant tissues with astonishing rapidity, sugars, and even starch, appearing in the tissues almost immediately after their exposure to light in the presence of carbon dioxide. Hence, any intermediate product, such as formaldehyde, is present in the cell for only very brief periods and in very small amounts. But small amounts of formaldehyde can often be detected in fresh green plant tissues and, as will be pointed out below, the whole process of photosynthesis, proceeding through formaldehyde as an intermediate product, can be successfully duplicated in vitro in the laboratory.

    No feature of a landscape gives us more pleasure than its flowers, over which poets have sung and artists have painted their most charming pictures, even a musician has composed a very beautiful piano piece, “To a Water Lily.” But their true place in the scheme of nature has a deeper significance: the wonderful color and symmetry of their parts, the plan of their arrangement, their transformation into curious forms, like the Madagascar orchid, and hundreds of others—all these point to their supreme function, an act of self-sacrifice comparable only to the fall of a leaf when its task is done. Petals, too, wither and die when the fertilized ovary, already a mother, begins the slow process of maturing its young and the end of the flowering stage is reached. Such a climax is this in certain plants that the whole plant dies, as we have already noted in the case of the century plant. The toddy or wine palm of India, often sixty or seventy years old and more than a hundred feet tall, flowers only once, and, as if in recognition of the fact that it has done that for which it grew, slowly dies as the seed ripens. More humble annuals, like buckwheat, and hundreds of others, live only one brief growing season, produce flowers and seeds, and then die, leaving behind them the only means of perpetuating their kind. The dormant seed carries over the winter the life they were themselves unable to maintain, as perennials and woody plants do in their buds.