The mechanism of carbon assimilation: Part III

Some experiments and conclusions recorded in two papers published in 1906 have been subjected to criticism by several investigators, and the present paper has been written with the object of presenting some new facts bearing on the problem of carbon assimilation, which incidentally support some of those conclusions. We also take this opportunity to restate the theory originally advanced, with such modifications as may be necessary, and to reply to a few of the more important objections to it which have been raised. The observations recorded below are concerned only with the initial stages of the photosynthetic process, that is to say, with the formation of the primary photolytic products from carbon dioxide, and with the evolution of oxygen. In the papers referred to some evidence was given in support of the belief that aqueous carbon dioxide is decomposed by light under the conditions obtaining in a green leaf, the immediate products of this decomposition being hydrogen peroxide and formaldehyde; and it is easy to see that the production of these two substances would satisfactorily account both for the oxygen and the carbohydrate, which are the first visible results of the natural process. As the evidence put forward was to some extent indirect, wholly so in the case of hydrogen peroxide, it was thought advisable to supplement it by further experiments.