CRITERIA AND METHODS 121 



mum total sugar content was found in February, and the 

 concentration rapidly decreased and became so depleted 

 shortly after blooming that its presence was not detected. 

 Sugar was not again found in measurable amounts until 

 August, from which time it gradually increased until leaf 

 fall. It is noteworthy that even at the maximum the total 

 sugar content was only 0.036 per cent (360 p.p.m.), and this 

 was found before there could have been an actively flowing 

 transpiration stream. It is true that he found a somewhat 

 higher concentration in the outer layers when radial dis- 

 tribution was investigated, but even the maximum here 

 observed was only 0.05 per cent (500 p.p.m.) and was found 

 early in April before any great leaf surface or transpirational 

 area could have been developed. From February to May, 

 the period of maximum sugar content in the outer layers, 

 the concentration averaged only 0.04 per cent. Anderssen's 

 suggestion, therefore, that the starch in the inner ring, when 

 hydrolyzed, is transferred along the medullary rays and 

 delivered into the outer tracheae, and the implication that 

 the xylem is an important channel for upward transport of 

 sugar find but little support in the evidence given. Mason 

 and Maskell (1931, p. 149; 1928a, p. 235) found that the 

 tracheal sap obtained from the cotton stem by water 

 displacement contained sugars at a concentration of 

 0.0155 to 0.0443 per cent (155 to 443 p.p.m.). This is of 

 the same order of concentration as found by Anderssen, yet 

 their experimental data rather conclusively demonstrate 

 that the xylem is not an effective channel for sugar trans- 

 port in the cotton plant. They also found the tracheal sap 

 of cotton to contain 0.01216 per cent total nitrogen, 

 0.01164 per cent calcium, and 0.00386 per cent phosphorus. 

 The presence of solutes in the exudation from plants at 

 periods when guttation is taking place is also evidence that 

 the vessels contain materials in solution. The concentra- 

 tion of this exudate is approximately the same as that of the 

 tracheal sap. Wilson (1923) found the exudate from maize 

 seedlings to contain as high as 0.1 per cent (1030 p.p.m.) 

 total solute, and timothy to contain from 0.022 to 



