METABOLIC PROCESSES IX THE PLANT. 349 



aqueous vapour under a bell-glass. All the leaves become almost 

 or completely devoid of starch. Microchemical tests for glucose 

 (for method see 115) show, as I have convinced myself, that in 

 the cells of the conducting sheath of the removed leaves much 

 sugar is present, while the corresponding cells of the leaves not 

 cut off contain but little sugar. 



We come to the conclusion that the conducting sheath of the 

 nerves is to be regarded as the tissue which effects the removal 

 from the leaves to other organs of the products of assimilation. 

 In many plants, e.g. Tropa3olum, the product of solution formed 

 from the starch, especially in the cells of the conducting sheath, 

 can easily be converted transitorily into starch. In other plants, 

 e.g. Impatiens, this is either not possible or only possible to a 

 limited extent. 1 



1 Literature : Sachs, Arbeit en des botanisches Instituts in Wiirzlnnj, Bd. 3, 

 Heft 1 (very important). Schitnper, Botan. Zeitnng, 1885, No. 47-49. 



140. Experiments with Branches. 



If in autumn, just after the fall of the leaves has begun, we 

 test for starch in branches or trunks of our trees several years old 

 (using the method indicated in 110), we find it present in the 

 tissues in large quantities, especially in the medullary rays, and 

 in the parenchyma of the wood and cortex. In Quercus and 

 Betula, etc., the pith also contains much starch ; in other cases 

 (e.g. in Corylus) the pith is devoid of starch. 1 The condition 

 of the trees or shrubs after the fall of the leaves we may designate 

 as that of autumnal starch maximum. The tissues of their stems 

 are then stocked with very copious quantities of reserve materials 

 which the leaves have produced. In many trees, however, certain 

 elements of the wood and cortex contain in autumn (and also in 

 summer) glucose as well as starch, a fact which is of especial 

 importance. To detect the glucose we use A. Fischer's method. 

 Pieces of branches are split along the middle, laid for five minutes 

 in a concentrated solution of Copper sulphate, washed with water, 

 and then put for two or three minutes in a boiling solution of 

 Sodium Potassium tartrate in soda lye. The necessary sections 

 are now readily prepared. In the glucose-containing elements a 

 precipitate of Cuprous oxide has formed. Generally it is not 



