34 PROXIMATE CONSTITUENTS OF PLANTS 



be taken every two minutes, and then at longer 

 intervals of time as the rate of change decreases. 



A curve should then be plotted showing the relation 

 between time and angle of rotation, the last time of 

 reading being about twenty-four hours after the 

 commencement of the inversion. 



The following results of an actual experiment are given : — 



The inversion of cane sugar being brought about by the action 

 of hydrogen ions, and the rate of inversion depending on the 

 concentration of hydrogen ions, a method similar to the above 

 can be used to determine the percentages of ionisation (strengths) 

 of different acids at various concentrations. 



Starch {fZ^^^O^^, 



Starch is produced in the leaves of all green plants, and is 

 stored in the seeds, roots, and tubers as a reserve food material 

 for the young plant before it is sufficiently far advanced in growth 

 to perform the functions of assimilation. 



Some plant products, such as rice (grain) and potatoes (tubers), 

 contain a sufficient amount of starch to serve as sources of this 

 substance and are largely grown for the purpose. 



