54 CARNEGIE INSTITUTION OF WASHINGTON. 



with leaves of the higher plants indicate that, unlike the animal, levulose is 

 not the most easily oxidized sugar. Under comparable conditions, levulose 

 produces a far lower respiratory activity than either d-glucose or sucrose. 

 Moreover, with levulose no stimulating effect of the amino-acids could be 

 detected; in fact, in many cases when amino-acids, together with levulose, are 

 given to the leaves, the respiration rates are lower than when this sugar is 

 given alone. 



The effect of d-mannose on higher plants has for some time been in dispute. 

 All of the experiments with this sugar not only showed no toxic effects, but 

 produced a relatively high rate of respiration. Similarly, the leaves given 

 d-mannose were appreciably stimulated in their respiration by amino-acids. 



In these investigations on the equilibrium and use of the various carbo- 

 hydrates the important points center about the glucose-levulose ratio. With 

 starch and sucrose as the form in which carbohydrates are most generally 

 stored in the plant, it is of fundamental importance to know first of all to 

 what extent each of the splitting products of starch and sucrose can serve the 

 plant in its metabolic economy and whether glucose and levulose are inter- 

 convertible in the plant. Also, it is essential to know to what extent the pro- 

 portion of these two sugars controls the formation of starch or sucrose. As 

 the latter two substances represent the most common form in which carbo- 

 hydrates are used commercially, this information has a very direct bearing on 

 a number of branches of agriculture. 



The continuation of these experiments is directed to establish the role which 

 each of these sugars plays in different processes of the plant and the conditions 

 governing starch and sucrose formation. 



These investigations, together with those on the carbohydrate-amino-acid 

 relation, offer the key to the interpretation of observations of long standing 

 which have never been adequately explained. Brown and Morris first reported 

 that the diastatic activity of leaves increased when these are kept in the dark. 

 The leaf, deprived of photosynthetic activity, is thus assured an ample supply 

 of hexose sugars for respiration while the store of starch lasts. This has com- 

 monly been given the teleological explanation that as the leaf needs more 

 sugar the starved protoplasm elaborates the means of obtaining it. On the 

 basis of the fact that leaves kept in the dark increase in amino-acids, together 

 with the observation of Sherman and his coworkers of the accelerating influ- 

 ence of amino-acids on diastatic activity, the phenomenon of increased dia- 

 static activity of leaves in the dark receives a rational explanation. Thus, an 

 increase in diastatic activity under these conditions simply means that the 

 amino-acids in the leaves had increased and thereby produced conditions 

 which are favorable to diastatic activity. 



Determination of Small Amounts of Various Sugars present in Leaves, 



by H. A. Spoehr and F. A. Cajori. 



In the first stages of the investigations on the carbohydrate metabolism 

 and equilibrium in plants, it was recognized that advance in this field is largely 

 dependent upon the development of analytical methods. The analysis of 

 plant material presents many extraordinary difficulties not encountered in 

 material of animal origin. This has necessitated the working out of a number 

 of new methods adapted to plant material. One of these, described in pub- 



