48 PHYSIOLOGY OF NUTRITION. 



on the one hand Helianthus leaves, and on the other Allium 

 leaves. The material is dried as quickly as possible in a large 

 drying charnber at about 80 C., then very finely ground and 

 freed from water at 100 C. About 5 gr. of dry substance are 

 treated in a beaker with 100 c.c. of water at 30 C., and after 

 digesting for a few hours, we filter off the solution, and carefully 

 wash the residue left on the filter-paper. The solution is made 

 np to 200 c.c. and divided into two portions. In 50 c.c. of one 

 we at once determine with Fehling's solution the quantity of re- 

 ducing sugar present. The second portion is heated for a good 

 time with a few drops of Hydrochloric acid, and then the quantity 

 of sugar in this is determined. For further details see Section III. 

 In this way we finally learn the quantity of reducing sugar in the 

 leaves before and not till after inversion respectively. In order 

 to determine also the quantity of starch in the leaves, the residue 

 on the filter is rinsed in a flask with 200 c.c. of water, and further 

 treated in the manner to be described in Section III. We finally 

 determine with Fehling's solution the quantity of sugar obtained, 

 and this serves as a measure of the quantity of starch in the 

 leaves. 3 



This method may also be employed in investigating the specific 

 energy of assimilation of leaves, or in studying the relationship 

 between assimilation in the leaves and conditions of illumination, 

 etc. We experiment, e.g., with the leaves of Helianthus or 

 Cucurbita. At five o'clock in the morning we remove one half 

 from a few of the leaves without injuring the midribs. W^e lay 

 the separated halves on a drawing board, cover them, with the 

 exception of the stronger nerves, with thin templates of wood, 

 about 50 or 100 sq. cm. in area, press these down, and with a 

 scalpel cut out corresponding areas of leaf. The second halves 

 of the leaves are not removed from the plant till after eight to 

 twelve hours of assimilatory activity, and are then treated like 

 the first, care being taken in each case to place the templates as 

 nearly as possible symmetrically with respect to their position 

 in the corresponding first removed halves. Immediately after 

 cutting out the areas of leaf, we rapidly dry them at 80 C. In 

 Helianthus annuus, 500 sq. c.c. of leaf surface weigh when dry 

 about 4 gr. 5-10 gr. of dry substance then serve for the deter- 

 mination of the quantity of carbohydrate present (sugar, starch), 

 and we shall find that the later cut halves are considerably richer 

 in these than the first, if the conditions of assimilation during the 



