CHAPTER II 



EVIDENCE FOR THE UPWARD TRANSPORT OF ORGANIC 

 MATTER THROUGH THE PHLOEM 



4. Ringing at Different Distances from the Tip and the 

 Transport of Carbohydrates Previously Stored in the 

 Xylem Region. — In many woody plants carbohydrates 

 are stored in large quantities in the tissues internal to the 

 cambium layer. In the older stems the wood parenchyma 

 and medullary ray cells are rich in stored carbohydrate, 

 while in the younger twigs the pith also is often well filled. 

 Just before bud break in the spring, not only do these living 

 cells in the xylem contain large quantities of soluble and 

 insoluble carbohydrates, but the water-conducting cells 

 themselves also contain soluble sugars, especially sucrose, 

 though in some trees small quantities of maltose and traces 

 or even appreciable quantities of hexose may also be 

 present. At this season the solution in the water-conduct- 

 ing tissues may, in some kinds of trees, reach a concen- 

 tration of as high as 2 to 4 per cent, or even occasionally 

 somewhat higher. Jones et al. (1903) report as high as 

 8 per cent sugar in the sap from the sugar maple. The 

 presence of this sugar solution at this season of the year 

 and its almost complete absence soon after the shoots have 

 grown have led to the seemingly logical conclusion, that this 

 solution of carbohydrates has been carried through the 

 xylem to the newly developing shoots, allowing for their 

 rapid growth in the spring. 



In order to determine whether the carbohydrates stored 

 in the xylem of woody twigs move up to the growing points 

 through the xylem with the water or through the phloem, 

 large numbers of twigs of several different species of woody 

 plants were ringed in the spring a short time before growth 

 started (Curtis, 1920a). The rings were made at different 



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