Page:Popular Science Monthly Volume 6.djvu/72

62 respiration. But, notwithstanding the discovery of a number of facts which tended to enlarge the province of this so-called nocturnal respiration, it was far from attaining the importance of the diurnal, which all the botanists held to be the true respiration of plants, and which, as compared with the other mode, clearly deserved this distinction, owing to the number, the duration, and the extension of the phenomena which it represented.

One might wonder at this strange duality of respirations in a single being—respirations that were antagonistic in their very essence; especially might one ask how plants could be deprived, during one-half of their life, of that physiological function, the unceasing performance of which would seem to be the most indispensable of all, to wit, the respiratory function—for this was held to be identical with the diurnal respiration; it might even be observed that certain plants, grown in the dark, perform this function very seldom; but, for all that, the facts all seemed to require the acceptance of the current theory.

These preliminary remarks will enable the reader fully to see the importance of the researches recently explained to the Lille Society of Sciences, by M. Corenwinder, of whose paper we propose to give a summary. The author, who has for twenty years pursued in one direction his studies of vegetal physiology, has proved that the nocturnal respiration of plants, though supposed to be exceptional, is in fact perfectly continuous, and constitutes their only true respiration. What hitherto has been called diurnal respiration, viz., the absorption of carbonic acid, the seat of which is the chlorophyll, instead of being the true respiratory phenomenon, is a phenomenon of assimilation and digestion, as pointed out by Claude Bernard. Plants and animals respire both in the same way. This is the grand fact, the proofs of which are given by Corenwinder.

Buds, young shoots, and nascent leaves, discharge a function hitherto insufficiently considered, but yet this function is of such a nature as to elucidate the most important laws of vegetal physiology. It may be readily shown by very simple experiments that, in this first period, and for a certain length of time, plants absorb oxygen unmistakably and uninterruptedly, exhaling carbonic acid. Nor is it only in the dark that they discharge this function; indeed, it is not very apparent during the night, when the weather is cold, as is often the case in spring. It is during the day, and when the sunlight is strongest, that this function becomes characteristic, and especially when the temperature is rising.

This is easily shown by placing delicate plants, gathered in the early stages of their growth, under a close bell-glass, connected with a receiver holding concentrated baryta-water, the receiver in turn being