94 PLANT PHYSIOLOGY 



The mere presence of a considerable amount of material for 

 respiration is not sufficient to provoke intensive respiration. In 

 dormant storage organs, fruits, bulbs, and rhizomes, with reserve 

 substances rich in sugars, the intensity of respiration is usually 

 very low. Blackman, who has given much attention during 

 recent years to the physiology of the storage of fruit, assumes 

 that in the case of dormant plant parts a special inhibitory sub- 

 stance is present that does not permit respiration to proceed at 

 a normal rate. He distinguishes two types of respirations. (1) 

 The '' flowing type" is determined by the presence of reserve 

 substances of a carbohydrate nature and consists in their oxida- 

 tion with liberation of carbon dioxide and water. (2) The 

 second type of ''protoplasmatic" respiration prevails in cases 

 when reserve substances are exhausted and respiration is hmited 

 by the decomposition of substances of the active protoplasm 

 itself. Such respiration serves to produce the minimum of free 

 energy necessary for the maintenance of life. 



A similar viewpoint had been previously advanced by Palladin, 

 who also assumed that protoplasm is the basic factor of respira- 

 tion. Proceeding from the fact that the proteins of the proto- 

 plasm and the nucleus (plastin, nucleoproteins) are digested by 

 pepsin with great difficulty, he made an attempt to compare 

 the intensity of respiration of the different organs of plants with 

 their content of proteins that are not digested by pepsin. In such 

 a simplified form, Palladin's hypothesis proved to be untenable, 

 and he was forced to reject this method of determining the amount 

 of active proteins. However, his original statement that it is 

 essential to distinguish the effect of the oxidizing mechanism 

 from the effects of oxidizable substances proved to be correct and 

 formed the basis of contemporary theories of respiration. 



Very abrupt changes in the intensity of respiration may be 

 observed under the influence of various toxic substances. In 

 small doses, nearly all such substances prove to be stimulating; 

 i.e., they increase the amount of carbon dioxide liberated. In 

 large doses, however, they are toxic to plants, and respiration 

 decreases rapidly. Special attention has been given to the 

 study of such anesthetics as ether, ethylene, and chloroform. 

 The same stimulative effect is displayed by a series of harmless 

 substances, such as neutral salts of alkalies and alkaline earth 

 metals, when applied in considerable concentrations. Such 



