Experimental results are at variance with the theory that chlorophyll acts as a sensitizer in bringing about a reduction of carbonic acid, after the analogy of eosin, which in the presence of light accelerates the decomposition of silver salts on photographic plates. Willstätter found that, when a colloidal solution of the pure extract of chlorophyll in water is exposed to sunlight and an atmosphere consisting of carbon dioxide exclusively, no formaldehyde is formed, but the chlorophyll is changed into yellow phæophytin owing to the removal of the magnesium from the chromogen group by the action of the carbonic acid. Jörgensen, on the other hand, discovered that in an atmosphere of pure oxygen, formaldehyde is formed, apparently by the splitting off and reduction of the phytyl ester of chlorophyll. Soon, however, the formaldehyde is oxidized to formic acid, which replaces the chlorophyllic magnesium with hydrogen, thus causing the green chlorophyll to degenerate into yellow phæophytin and finally to lose its color altogether. The dissociation of the chromogen group may be due to the fact that the reaction takes place _in vitro_, and may not occur in the living plant. At all events, it would seem that plants, like animals, manufacture carbohydrates by a destructive rather than a constructive process, and that water and carbon dioxide serve rather as materials for the regeneration of chlorophyll than as materials out of which sugars are directly synthesized. A new theory has been proposed by Dr. Oskar Baudisch, who seems to have sensed the irrelevance of the formaldehyde hypothesis, and to have sought another solution in connection with the chromogen group of chlorophyll. He finds a more promising starting-point in formaldoxime, which, he claims, readily unites with such metals as magnesium and iron and with formaldehyde, in the presence of light containing ultra-violet rays, to form organic compounds analogous to the chromogen complexes in chlorophyll and hæmoglobin. Oximes are compounds formed by the condensation of one molecule of an aldehyde with one molecule of hydroxylamine (NH₂OH) and the elimination of a molecule of water. Hence Dr. Baudisch imagines that, given formaldoxime (H₂C:N·OH), magnesium, and ultra-violet rays, we might expect a spontaneous formation of chlorophyll leading eventually to the production of organic life. “It is his theory that life may have been caused through the direct action of sunlight upon water, air, and carbon dioxide in the ancient geologic past when, he believes, sunlight was more intense and contained more ultra-violet light and the air contained more water vapor and carbon dioxide than at the present time.” (_Science_, April 6, 1923, Supplement XII.)