RELATION OF ANNUAL RINGS TO THE LEAVES 113 



The tracheal elements of the new shoot (new stem and leaves) 

 have direct communication with the roots through the tra- 

 cheal elements of the new ring of growth which the cambium 

 adds along the whole stem. It often happens, however, that 

 before the cambium has made this connection the leaves are 

 already well along in their development and are drawing water 

 through the channels of the older wood. How this is accom- 

 plished will be seen in Fig. 57. In this figure the spiral and 

 annular tracheal elements are represented by a spiral line, the 

 current ring of growth is the outermost zone with the ascending 

 arrows and the older annular rings are between this and the 

 pith. It will be seen that the first-formed tracheal elements 

 (the spiral lines in the figure) from the leaf join with those of 

 the current year's segment of stem. It will be seen also that 

 the first-formed tracheal elements in last year's segment of stem, 

 as well as of preceding years, have broken apart and presum- 

 ably can be no longer functional. Before the cambium be- 

 comes active in the new shoot practically all of the water which 

 the leaves get must be drawn through the small spiral and an- 

 nular tubes of the new shoot from the tracheal elements of last 

 year's growth. When the cambium begins its activity it forms 

 new tracheal elements in the new shoot which unite with the 

 tracheal tissues from the leaf and pursue a continuous course 

 through the new ring of growth all the way down the stem and 

 into the roots (Fig. 57). 



Relation of Annual Rings to the Leaves. A study of the 

 diagram, Fig. 57, will show how the tracheal elements from 

 the leaves have most extensive and direct connection with the 

 tracheal elements formed by the cambium the current year, 

 and therefore the great advantage to water-conduction which 

 comes from the formation, first of all, of large tracheal ele- 

 ments in this new growth. 



Experiments with eosin and other aniline dye solutions have 

 shown that water rises throughout the sapwood, but most rap- 

 idly in the newest rings, and that if the latter are cut through 

 the older rings are then employed to carry the water past the 



