Carbon Assimilation. 
2 l I 
which removed about 97%. to 98% of the sugars. 
Davis, Daish and Sawyer (1916) consider this method of treat¬ 
ment is unsatisfactory in the case of moderately thick leaves such 
as that of the mangold, where heating up may be slow and a certain 
amount of enzyme action is possible before the enzymes are 
destroyed. They therefore adopt the following method in their 
work. About 1 kilo, of freshly picked leaf material is dropped in 
small quantities at a time into 2 litres of boiling 95% alcohol con¬ 
tained in a large zinc beaker to which 20 c.c. of ammonia of S.G. 
0 880 is added in order to neutralise the acids present in the leaf. 
After boiling the alcohol for half an hour the further extraction of 
the alcohol-soluble contents of the leaf is carried out in an extraction 
apparatus on the principle of the Soxhlet extractor. The extraction 
is complete after 12 or 18 hours. The final separation of the 
extract from the residue is effected in a Buchner press. The 
residue is dried on paper trays in a steam oven for 18 hours and 
from it the total insoluble matter, the starch and pentosans are 
estimated. The alcoholic extract is analysed for total soluble 
matter, sucrose, maltose, glucose, fructose, and pentoses. It can 
be kept in a waxed-corked bottle for 3 to 6 months without any 
change occurring in the sugars if about 10 c.c. to 20 c.c. of toluene 
are added. 
2. Estimation of Starch. 
Brown and Morris estimated the starch in their dry leaf powder 
by O’Sullivan’s method (1884) which consists in converting the 
starch into a mixture of dextrin and maltose by means of diastase. 
The leaf material usually contains tannins, amino-acids, etc. which 
influence the optical activity and reducing power of a solution and 
these accompanying substances have therefore to be removed by 
precipitation by means of basic lead acetate. Davis and Daish 
(1914) find that this method does not give correct results 
because some of the dextrin is carried down with the precipitate 
and so is lost to the analysis. It is estimated that as a result 
of this the starch estimations in leaf material made by O’Sullivan’s 
method may be 15% to 20% below the actual starch content. 
Davis and Daish therefore treat the plant material with taka- 
diastase which converts starch wholly into maltose and dextrose 
which are then estimated by measurement of the cupric reducing 
power and the optical activity. The leaf material is first treated 
for 24 hours at 38 n C with about 20 times its weight of water con- 
