220 BOTANY 



substance in the same way as upon an easily oxidised body. But the discovery of 

 intramolecular respiration led to a new conception of the processes of normal 

 respiration. According to it, the protoplasm seems by its vital activity constantly 

 to produce one or more substances which greedily seize upon oxygen. The aflinity 

 of these substances for oxygen is so great that, in case no free oxygen is at their 

 disposal, they decompose and take it from the protoplasmic substance itself (just 

 as chlorine has the power of decomposing other compounds to combine with 

 hydrogen). Plants breathe, accordingly, not as a result of the decomposing 

 oxidation of the oxygen in the air, but they absorb oxygen because respiration is 

 essential to the performance of those metabolic processes on the continuance of 

 which their own vitality depends. Respiration, like nutrition and growth, 



IS AN EXPRESSION OF A PARTICULAR VITAL ACTIVITY OF THE PROTOPLASM. From 

 this standpoint, it is at once evident that respiration becomes intensified with every 

 increase in the vital activity, and on the other hand, decreases with every diminu- 

 tion of the vital functions. 



To understand the physiological reason or the existence of such a vital pro- 

 cess as respiration is more difficult. The behaviour of plants in an atmosphere 

 free from oxygen demonstrates, at all events, that normal respiration is requisite 

 for the vital activity of the protoplasm ; that, through it, in a word, the equilibrium 

 of the living substance is disturbed, and so the stimulus given to further mole- 

 cular movements and renewed vital activity. Through the disturbing activity 

 of respiration, the energy of the protoplasm is continually aroused, and 

 the latent forces, accumulated through the operation of the vital processes, are 

 again set free : it is, in other words, the specific source of all vital energy. In 

 intramolecular respiration, the necessity for oxygen disturbs the equilibrium in 

 an unnatural way, and sets free forces, which lead, not to the continuance of the 

 vital activity, but to the destruction of the living substance. 



That specific vital energy can be otherwise derived than through the utilisation 

 of free oxygen is shown in the case of the Anaerobionts (p. 213), which live and 

 multiply without the presence of free oxygen. The formation of ferric hydroxide 

 by the so-called iron bacteria, as well as the production of sulphuric acid by the 

 sulphur bacteria, is probably the result of an attempt on the part of those micro- 

 organisms to substitute other sources of energy for normal respiration. 



The energy gained by the absorption of oxygen is accompanied by 

 a loss of combustible organic substances. This loss is first felt by the 

 protoplasmic body itself, but is soon made good again at the expense 

 of the carbohydrates and fats ; so that no permanent loss of 

 protoplasmic substance from respiration is perceptible, but A VISIBLE 



DIMINUTION OF THE CARBOHYDRATES AND FATS CAN BE DETECTED. 



Heat produced by Respiration. — Respiration is, chemically and 

 physically considered, a process of oxidation or combustion, and, like 

 them, is accompanied by an evolution of heat. That this evolution 

 of heat by plants is not perceptible is due to the fact that considerable 

 quantities of heat are rendered latent by transpiration, so that 

 transpiring plants are usually cooler than their environment ; and also 

 to the fact that plants possess very large radiating surfaces in propor- 

 tion to their mass. The spontaneous evolution of heat is easily shown 

 experimentally, if transpiration and the loss of heat by radiation are 

 prevented and vigorously respiring plants are selected. Germinating 



