THE FUNCTIONS OF THE WOOD 187 



In 1888 A. Fisher demonstrated by chemical means 

 the presence of reducing sugars in the tracheae of a large 

 number of trees at various times of the year. He does not 

 appear to have tested for sucrose. 



From this it might be inferred that the conveyance 

 of carbohydrates in the wood described by Hartig, and 

 supposed to occur noticeably only in spring, in reality 

 takes place all the year round, but in spring most 

 markedly. 



Notwithstanding this, it is surprising to find how Sachs's 

 (1887) statement that the water in the tracheae is "an 

 exceedingly dilute solution of these (nutritive) salts, which 

 may be compared at once to. ordinary drinking-water/' 

 seems to have won the ear of writers; so that tne function 

 of the tracheae in conveying organic substances upward 

 is either ignored in text-books and omitted from the con- 

 sideration of plant physiologists, or its continuance 

 throughout the year is discredited or left doubtful; as, 

 for example, by Jost (1907), and in the cautious statement 

 of Haberlandt (1914). 



Leclerc du Sablon (1902), however, investigated the 

 seasonal variations in the reserve materials of the stems 

 and roots of trees, and has recently (1911) summarized his 

 researches. His analyses deal with the total contents of 

 the wood, both of cells and tracheae. He clearly points 

 out the function of the wood parenchyma cells in mobilizing 

 reserve carbohydrates, which are then passed upwards by 

 the elements of the wood, and to some extent by the 

 bast also. Since these investigations are already in an 

 accessible form, they will not be considered here at any 

 length. Nicoloff (1911) has also given a very good 

 account of the functions of the medullary rays and of 

 the tracheae. 



