Respiration of Plants and Animals. 25 



with oxidizable substances. Cahours (op. cit.) and others 

 often since have found that fruits, during their period of 

 growth, appropriate carbon and give off* oxygen, Uke other 

 green parts of the plant; but that when ripening they 

 cease to do so, and begin to inhale oxygen and give off 

 carbonic acid ; the chemical changes taking place during the 

 process of maturation being essentially oxidation phenomena. 

 It is also well established that many fruits, such as the apple, 

 the pear, and the orange, continue the maturation process 

 after separation from the parent stem, acting in a manner like 

 independent organisms. If placed in a close vessel contain- 

 ing air, a portion of the oxygen gradually disappears, and is 

 replaced by carbonic acid. A difficulty was felt by Cahours 

 in explaining the continued exhalation of CO.^ from fruits 

 enclosed in an atmosphere of nitrogen or hydrogen, which he 

 could ascribe only to some fermentation. Fremy, in a note 

 to the communication of Cahours, tries to explain it as being 

 due to the slow process of combustion going on in the 

 interior of the fruit, which is no doubt true ; but is at the 

 same time rather an insufficient explanation, without some 

 account such as is here given of the state in which the 

 oxygen exists while that slow combustion is going on, the 

 full explantion being that the oxygen is stored up in loose 

 combination, to be given off as required for the formation of 

 oxidation products and among them COg. 



With reference to the substance with which the oxygen is 

 temporarily combined I cannot speak very definitely ; it is 

 certain, however, that in fresh fruits and other vesfetable 

 substances there is an element which is possessed of the 

 same ozone-transferring property as haemoglobin. If a fresh 

 section does not supply spontaneously the blue colour on 

 the application of tincture of guaiacum, it can be brought 

 out by the addition of a drop of solution of peroxide of 

 hydrogen ; and if it had appeared spontaneously, the peroxide 

 has the effect of rendering the blae more intense. I have 

 found that in fruits, when long-kept, the ozone reaction 

 is gradually enfeebled, the power of inhaling oxygen 

 being lost and the amount stored up gTadually con- 

 sumed. On the other hand, the ozone- transferrer may still 

 be detected when the fruit has become over-ripe and has 

 entered on the stage of incipient decay, disappearing 

 entirely, however, in parts which have become actually 

 rotten. When fruits, &c., are cooked either with moist or 

 dry heat, both this substance and the active oxygen are 



