230 ENZYMES AND 



nutrition of protoplasm. It is however changed by the 

 enzyme invertase or invertin into a mixture of dextrose and 

 levulose, both of which sugars possess immediate nutritive value. 

 In roots, such as sugar-beet and carrot, a great part of the 

 organic material manufactured in the leaves during the first 

 year of growth is sent down to the root and stored in the form 

 of cane-sugar. This reserve-material is utilised during the 

 second year for the production of new stems, flowers and 

 seeds, but before transmission from the root to the seats of re- 

 newed growth, the enzyme invertase decomposes the cane-sugar 

 into dextrose and levulose according to the following equation : — 



C12H22O11 + HjO = C5Hj20g + CgHijOg 



cane-sugar water dextrose levulose 



This form of decomposition of a compound which involves 

 the fixation of the elements of water is termed hydrolysis or 

 hydrolytic decomposition, and is characteristic of the action of 

 the majority of enzymes of all kinds. 



Invertase has been found in leaves, in the roots of young 

 plants, in germinating pollen-grains, and in other portions of 

 plants where cane-sugar is present. 



(iv) Certain substances known as glucosides occur commonly 

 in plant-tissues : their exact function and nutritive value to the 

 plant are not yet understood. However, under the influence of 

 acids and special enzymes, they are hydrolysed into useful 

 sugars and other bodies, usually aldehydes or phenols. 



The sugar produced is generally dextrose (glucose), hence 

 the term glucoside applied to such compounds. 



The best known examples are amygdalin, present in many 

 rosaceous plants (see p. 388), sinigrin, abundant in mustard and 

 other Cruciferse (see p. 380), and salicin in the willow. Some ot 

 the astringent compounds so widely distributed in all parts of 

 plants and known as tannins are also glucosides. 



The decomposition of amygdalin is effected by the enzyme 



