178 FUNDAMENTALS OF FRUIT PRODUCTION 



Increasing Osmotic Concentration. — Sugars are important to the 

 plant because they are osmotically active. Since the osmotic concen- 

 tration depends on the number of molecules and not on their size, it is 

 evident that the formation of disaccharides from simple sugars reduces 

 the osmotic concentration. Conversely, the hydrolysis of compound 

 sugars or polysaccharides to simple sugars increases the osmotic concen- 

 tration. Thus the building up and splitting down of carbohydrates 

 regulates the osmotic concentration. On the other hand, it unques- 

 tionabl}^ plays an important part in controlling synthetic and hydrolytic 

 processes. Thus compound sugars and especially starch are usually 

 produced wherever the concentration of sugars is high, though other 

 factors are involved, particularly enzymes. The hydrolysis of compound 

 carbohydrates proceeds most rapidly when the concentration of sugars 

 is low; therefore their consumption in respiration, their removal to other 

 organs and their use in the formation of other compounds, particularly 

 of substances like cellulose that are insoluble and consequently not 

 involved in the osmotic system, accelerate the processes of hydrolysis. 



As a Source of Energy. — One of the most important properties of 

 carbohydrates is that of yielding energy in the process of respiration. In 

 fact most of the energy used by plants and animals is the stored potential 

 energy of fats and carbohydrates. By means of carbohydrates the roots 

 are able to utilize the energy of sunlight. 



Respiration involves several processes. There are many theories, but 

 according to the most suggestive, respiration consists of two main reac- 

 tions; one is a process of cleavage, in which the simple carbohydrate 

 molecule is split into carbon dioxide and certain intermediate substances, 

 probably alcohols or acids; the other is a process of oxidation, in which 

 these intermediate substances are oxidized to carbon dioxide and water. 

 The first process is essentially a fermentation for which the enzyme, 

 zymase, is essential. The second process — of oxidation — depends on 

 enzymes called peroxidases which act only in the presence of peroxides. 

 Peroxidases supposedly transfer oxygen from organic peroxides to the 

 products of cleavage formed during the first process in respiration, 

 oxidizing them to carbon dioxide and water. According to some investi- 

 gators there are other enzymes involved but if this be true, they play 

 subsidiary parts and need not be considered here. 



In general the amount of carbon dioxide given off is approximately 

 equal to the amount of oxygen used in respiration so that the respiration 

 of a hexose may be represented by the formula C6H12O6 + 6O2 = 6H2O 

 + 6CO2 + energy. The two processes of respiration, cleavage and 

 oxidation, are more or less independent of each other, so that an accumu- 

 lation of acid may occur in plant tissues during periods of active respira- 

 tion, through the incomplete oxidation of carbohydrates and other sub- 

 stances. The inverse correlation existing between starch content and 



