250 VEGETABLE PHYSIOLOGY 



takes place in the plant is uncertain, but it is clear that the 

 starch, which is insoluble, is converted into sugar, which 

 can be removed to the parts of the plant where it is 

 required for building up the protoplasm. 



Inulase occurs in the tubers and tuberous roots of 

 some of the Composite, in the bulbs of certain Monocoty- 

 ledons, and in some of the Fungi. It converts inulin 

 ultimately into levulose or fructose, but the action is not 

 a very simple one, at least one intermediate body being 

 formed during the process. 



Invertase has a much wider distribution. It is easily 

 extracted from the Yeast-plant, in which it is present in 

 relatively considerable quantity. Other fungi which con- 

 tain it are Fusarium and Aspergillus, besides certain 

 bacteria. . In flowering plants it has been found in seeds, 

 buds, leaves, stems, roots, and pollen grains. Its action 

 is the hydrolysis of cane-sugar, which it splits up into 

 glucose and fructose, according to the equation 



C.AA, + H 2 = C 6 H 12 6 + C 6 H, 2 6 



Cane-sugar Water Glucose Fructose 



It is a little difficult to understand why this decomposition 

 of cane-sugar is necessary, as it can diffuse through 

 membranes, and in many cases it has been found capable 

 of assimilation by the protoplasm. Probably, however, 

 each of the sugars concerned in the transformation has a 

 special part to play in the metabolism of the plant, and 

 neither can readily replace either of the others. 



Glucase occurs in the grains of various cereals, being 

 especially prominent in the Maize. It is also fairly 

 abundant in the Yeast-plant. It has no action on cane- 

 sugar, but splits up maltose into glucose, one molecule of 

 the former taking up water and yielding at once two 

 molecules of the latter. 



Other sugars of similar constitution to maltose and 

 cane-sugar are made to undergo similar transformations 

 by enzymes of less widespread distribution. The chief of 

 these are trehalase, melibiase, melizitase, and lactase^ 



