1 10 Carbon Assimilation. 



taining 1% by volume of toluene which removes certain optically 

 active leaf substances, among them dextrin if it is present. The 

 residue, say 10 grams, containing the true starch, is then boiled with 

 200 c.c. of water to gelatinise the starch. It is then left for 24 hours at 

 38"C after addition of 0-1 gram of taka-diastase and 2 c.c. of toluene. 

 After destroying the enzyme with 2 drops of concentrated sodium 

 hydroxide and filtering, basic lead acetate is added (about 2-5 c.c.) 

 and the volume made up to 500 c.c. The slight excess of lead is 

 removed by the addition of the exact quantity of solid sodium 

 carbonate necessary. After filtration the reducing power and optical 

 rotation of the solution are determined. From these values the 

 quantity of starch is calculated on the assumption that the only 

 reducing and optically active substances present are glucose and 

 maltose. In measuring the cupric-reducing power of all sugars 

 examined the standard conditions laid down by Brown, Morris and 

 JVlillar (1897) are employed, and their tables of the reducing power 

 of maltose, glucose and fructose used. Similar tables for /-arabinose 

 and /-xylose have been compiled by Daish (1914). 



3. Estimation of Dextrin (" Soluble Starch "). 



It was found by Davis and Sawyer (1916) that the leaf material 

 from potato, after extraction with 80% alcohol contains large 

 quantities of a substance readily soluble in water and having a high 

 positive optical rotation. This and the reducing power were 

 determined, and again after treatment with taka-diastase and basic 

 lead acetate, and from the change in reducing power and rotation 

 thus brought about, the dextrin was calculated. 



4. Estimation of Pentosans. 



These were estimated by Davis, Daish and Sawyer by distilling 

 1-0 to 1-5 gram of the oven-dried leaf material with hydrochloric 

 acid by the Krober-ToUens method and weighing the furfural 

 produced as phloroglucide. 



5. Preparation of the Leaf Extract for Estimation of Sugars.' 



Before estimating the sugars in the leaf extract containing 

 them, the alcohol in the case of an alcoholic extract is replaced by 

 water by evaporation of the alcohol and subsequent dilution with 

 water. Davis, Daish and Sawyer evaporate the alcohol under 

 reduced pressure (20-30 mm.) in a special distillation apparatus 

 (Davis, 1913). By this means 3 litres of extract is reduced to 150 c.c. 

 and diluted with water to 500 c.c, a little hot alcohol or toluene 



