THE FUNCTIONS OF THE WOOD 213 



nounced differentiation of their medullary rays (^Esculus, 

 Tilia, etc.). . . . If the solution of starch takes place in 

 the order indicated, the conclusion can be drawn that the 

 upright cells, other than those in contact with the vessels, 

 are to be regarded as forming a storage tissue, whereas 

 the radially elongated cells serve principally as channels 

 for the conduction of foodstuffs." 



Nicoloff further remarks upon the scarcity of glucose in 

 the medullary ray cells, as shown by the copper-reducing 

 test, although it may be found in the wood parenchyma and 

 fibres, and especially in the vessels. This absence of sugar 

 he thinks remarkable in view of the high osmotic pressures 

 found by Kny (1909) in the ray cells. To the writer it 

 appears that the presence of sucrose sufficiently accounts 

 for the pressures. Curiously enough, Fischer makes no 

 mention of testing for this sugar by inversion, and Nicoloff 

 in this respect followed faithfully in his steps. As already 

 pointed out, sucrose is by far the most abundant of all 

 the sugars in many woody stems. 



The researches of the earlier physiologists (Th. Hartig, 

 Reichard, Schroder, N. J. C. Muller, Russow, Grebnitzky, 

 Baranetzky, and A. Fischer) upon the starch of the 

 wood and its transformations have been considered in 

 detail by Strasburger (1891). 



SUMMARY. 



1. Sugars (monosaccharides and disaccharides, or both) 

 are found at all times in the sap in the tracheae of the trees 

 examined, and usually in greater quantities than elec- 

 trolytes. 



2. The greatest concentration of the sugars occurs in 

 the early spring; this is followed by a rapid dilution in 

 spring and early summer, so that a minimum occurs in the 

 summer or autumn. A rise in concentration, slow at first, 



