276 BOTANY PART i 



plants (p. 271), would be fermentations. Lastly, the processes of de- 

 nitrification and of reduction of sulphates, in which anaerobic bacteria 

 probably in order to obtain oxygen reduce nitrates to free nitrogen 

 and sulphates to sulphuretted hydrogen, cannot be excluded from 

 fermentations. 



Many fermentations have another significance besides that of 

 obtaining energy. The products of fermentation such as alcohol, 

 acids, etc., are poisons ; they are, as a rule, more injurious to other 

 organisms than they are to those which produce them. On this 

 account they are suited to exclude other organisms from the supply 

 of food-material. It is true that a fermentation organism in a pure 

 culture on a definite substratum renders, by the products of its meta- 

 bolism, the latter not only unsuitable to concurrent organisms but 

 sooner or later for itself. When organic material, as is the case in 

 nature with the remains of dead organisms, is the prey of various 

 micro-organisms these co-operate in their action ; metabolic products 

 of one kind of micro-organism are further decomposed by others until 

 the organic compounds are converted into inorganic or mineral sub- 

 stances. The final products are water, hydrogen, methane, ammonia, 

 nitrogen, and sulphuretted hydrogen. 



Circulation of Material. All these end-products of fermentation 

 can be utilised by other organisms. Leaving C0 2 and H 9 aside as 

 having been sufficiently dealt with, it may be noted that hydrogen, 

 methane, ammonia, and sulphuretted hydrogen are all oxidised by 

 particular bacteria, while others assimilate nitrogen. It is only by 

 this co-operation of all organisms that life is maintained on the earth 

 and substances again brought into circulation. If only one type 

 of organism existed, it would in a short time have destroyed the 

 possibility of its own existence by its one-sided metabolism. 



D. PRODUCTION OF HEAT AND LIGHT IN RESPIRATION 

 AND FERMENTATION 



Heat ( 50 ). Since typical respiration is a process of oxidation, it is 

 easy to understand that it is accompanied by an evolution of heat. That 

 this evolution of heat by plants is not perceptible is due to the fact 

 that it is not sufficiently great, and that considerable quantities of heat 

 are rendered latent by transpiration, so that transpiring plants are 

 usually cooler than their environment. In some fermentations, e.g. 

 alcoholic fermentation, a considerable quantity of heat is evolved. 

 The heat of rotting manure is well known and employed in the con- 

 struction of hot-beds. 



The spontaneous evolution of heat is easily shown experimentally, if tran- 

 spiration and the loss of heat by radiation are prevented and vigorously-respiring 

 plants are selected. A quantity of germinating seeds (peas) shows under proper 



