I 



CHAPTER II. — SPECIAL PHYSIOLOGY OF THE NUTRITIVE FUNCTIONS. 731 



c. Plants which do not possess chlorophyll are unable to absorb 

 kinetic energy in the form of light, bat they obtain their supply 

 in other waySr ^^^or instance, it has been pointed out (p. 711) 

 that these plants require more or less complex carbon-compounds 

 as food : the significance of this fact is not only that these plants 

 are unable to produce these compounds for themselves from carbon 

 dioxide and water, but further, that these compounds represent 

 potential energy which, in the decomposition of these compounds 

 in the body of the plant, is evolved in the kinetic form : hence 

 these organic food-substances supply the plants not merely with 

 matter, but also with energy. 



Plants without chlorophyll also obtain energy by yet other means. For 

 instance, when sugar is fermented by Yeast (see p. 723), there is a considerable 

 evolution of energy, and this is the true significance of the process from the 

 point of view of the Yeast-plaat : similarly, Bacteria cause various putrefac- 

 tive and other fermentations which are attended by an evolution of energy. 

 In these cases it would appear that the plant avails itself of the kinetic energy 

 evolved in the fermentative process. 



A few cases have been investigated among Schizomycetes in which the supply 

 of kinetic energy is obtained by oxidative processes: this occurs, for instance, 

 in the case of the nitrifying organisms (Nitrobacteria) which oxidise ammonia 

 compounds to nitrites, and nitrites to nitrates, in the soil : in the case of the 

 Sulplwhacteria which oxidise hydrogen sulphide (H2S) with the formation of 

 sulphates : and io the case of the Ferrobacteria which oxidise ferrous to ferric 

 salts (see p. 719). 



The energy obtained in any of these ways is of primary impor- 

 tance in the anabolism of the plant : it is concerned with the 

 building up of more and more complex organic compounds and 

 with the nutrition of the protoplasm ; and in as far as these com- 

 pounds, such as carbohydrates, proteids, etc., accumulate in the 

 plant, in so far is potential energy accumulated likewise. But, 

 inasmuch as the catabolic processes are at the same time in con- 

 stant operation, there is going on in the plant a constant conversion 

 of potential into kinetic energy, a considerable proportion of which 

 is dissipated or lost to the plant. 



Energy is most commonly d issipat ed in the form of heat, in a 

 few cases in the form of li^t, and also commonly in the form of 

 movement. The evolution of heat by plants is not usually 

 sufficient to cause the temperature of the plant-body to be higher 

 than that of the surrounding air. This is partly due to the fact 

 that the catabolic processes of plants are not generally very active, 

 and partly to the continual loss of heat by radiation and in con- 



