The Respiration of Plants

Abstract

I DESIRE, with your permission, to give publicity in the columns of NATURE to the results of some observations on the above subject, communicated by me to the Royal Society of Victoria on June 13. As the facts to be mentioned are not referred to in Sachs' “Text-book of Botany”, in the dictionaries of chemistry of Watts and Wurtz, or in recent volumes of the Journal of the Chemical Society or the Chemisches Centralblatt, I presume that they are little, if at all, known to botanists. I have found, first about nine years ago, and have more systematically observed lately, that fresh sections of many fruits, such as the apple and pear, and other vegetable structures as the potato, turnip, &c., give the reactions considered to be characteristic of ozone, viz., causing separation of iodine from iodide of potassium, and turning tincture of guaiacum blue, the intensity of these reactions varying in different samples of the vegetable substances, but depending mainly on their comparative freshness. I have further found that the same structures contain a substance which acts as an Ozonträger, to use Schönbein's expression, a substance which transfers ozone from peroxide of hydrogen and similar articles. This is shown by the fact that if the guaiacum is not blued at all, or only to a slight extent, the blue colour becomes very marked when a drop of ethereal solution of peroxide of hydrogen is added. I infer from these observations (1) that the oxygen inhaled by living plants, and even by pulled fruits for a time, is ozonised or rendered active, probably by entering into loose combination, as is the case with the oxygen in the blood of animals; and (2) that it is probable, though not proved, that the ozone-transferring substance existing in almost every fresh vegetable structure is that with which it is loosely combined, as the oxygen in the blood is with the hæmoglobin of the red corpuscles, which is a very active Ozonträger. This element in plants is gradually destroyed as decay comes on, and ceases to perform its ozone transferring function when the fruit, &c., containing it is cooked. It is not chlorophyll, as is shown by its situation, and it seems to be intimately associated with the vascular tissue. From analogy with the animal substances hæmoglobin, fibrin, myosin, &c., which have a similar action, it may be presumed to be proteinaceous, though I am unable to indicate its chemical and other characters more exactly. The interesting analogy between the respiratory functions of animals and plants indicated by these observations will, I hope, be considered a sufficient excuse if I ask you to insert this short summary of my paper which you will receive at the same time.