in ASCENT OF SAP IN STEMS 59 



reciprocals of the resistances measured in ohms) indicate 

 the relative richness of the saps in electrolytes. 1 From 

 the table it appears that the concentration of electrolytes 

 has become four to six times greater by steaming. The 

 development of strong acidity during the heating (observed 

 in every case so far examined) shows that the increase of 

 electrolytes is partly due to the introduction of acids into 

 the sap. 2 In Fagus and Populus an oxydase was present 3 

 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 oxydase was not 

 looked for in the case of Ilex. 



Qualitative tests on the sugars of the saps from the fresh 

 and steamed branches indicated changes in these bodies also. 

 Where non-reducing sugars are present, they are, of 

 course, hydrolysed by the steaming of the branch, and the 

 acid liberated ; and they appear after the heating as reducing 

 sugars. Examples of this were found in Ilex aquifolium, 

 Salix babylonica, and Cotoneaster frigida. In the last- 

 mentioned, however, larger quantities of reducing sugars 

 were found present in the sap of the steamed branch 

 than could have been formed by the inversion of the non- 

 reducing sugars present in the sap of the fresh branch, so 

 that we must assume that they were introduced into the 

 sap from the neighbouring cells. 



These tests are sufficient to substantiate the surmise that 

 the physical and chemical nature of the sap is profoundly 

 altered by steaming the branch through which it passes. 



It is evident that the substances thus introduced into 

 the sap must be swept along in the rising current till they 

 reach the leaves, except for what material is absorbed by 



1 I am indebted to Mr. W. R. G. Atkins for the 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 ends of the pieces. 



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



