Dixon — Changes in the Sap by the Heating of Branches. 225 



rotation is collected. The quantities of sap obtained in this way are sur- 

 prising. Whether in midsummer, autumn, or winter, I ha-ve found that 

 four such pieces of the various woods used yielded about 3-5 c.c. In the 

 same way sap was collected from pieces of steamed branches. These samples 

 of sap could now be compared physically and chemically. In every ease, as 

 was anticipated, profound differences were found to exist between the 

 characters of tlie saps drawn from the fresh and the steamed branches. 

 Some of the results may be seen in the following table : under A the 

 depression of the freezing-point, under C the conductivity is given. Also the 

 reaction of the sap to litmus and the presence of oxydase are noted. 



The change in A brought about by steaming is due to the total increase 

 of tlie dissolved substances, and indicates that the concentration of the sap 

 has increased 4-6 times. The changes in conductivity (expressed as the 

 reciprocals of the resistances measured in ohms) indicate the relative richness 

 of tlie saps in electrolytes.' From the table it appears that the concentration 

 of electrolytes has become 4-6 times greater by steaming. The development 

 of strong acidity during the heating (observed in every case so far examined) 

 shows that the increase of solutes is partly due to the introduction of acids 

 into the sap.^ In Fagus and Populus an oxydase was present' in the sap 

 of the unsteamed stem, which coloured guaiacum tincture faintly blue. The 

 blue was intensified by the addition of hydrogen peroxide. The oxydase 

 was of course destroyed with heating. The oxydases were not looked for in 

 the fresh sap of Ilex. 



Qualitative tests on the sugars of tlie saps from the fresh and steamed 

 branches indicated changes in these bodies also. 



Where uon-reduciug sugars are present, they are of course hydrolysed 

 during the steaming of the branch by the acid liberated, and appear after the 

 heating as reducing sugars; examples of this were found in Ikx Aquifolium, 



1 I am indebted to Mr. W. R. G. Atkins for tbe determination of these conductivities. 

 ^ The very faint acidity of the sap from the fresh branches may probably be ascribed to the sap 

 set free from the injured cells at the ends of the pieces. 



^ It is possible that this oxydase was also derived from the cut cells. 



