36 



Growth 



intensively in the size (chiefly length) of cells in the xylem of woody 

 plants. 



Sanio ( 1872, 1873), working with pine, was the first to attack this prob- 

 lem intensively. He came to several general conclusions, the more impor- 

 tant of which are the following: 



1. Tracheids increase in length from the center of the trunk or branch 

 toward the outside through a number of annual rings but finally reach a 

 constant size. 



75 - 



r/o 



• 65 



;6o 



£55 



50 



36 



32 

 28 



g24 



E 



O 



S 20 



C 



= 16 



c 

 c 



< 12 



10 



20 



30 



Age in years 



40 



50 



925 

 900 



875 



i 

 850.S 



.c 



825 I 5 

 o> 



800 5 

 775 

 750 

 725 



Fig. 3-9. Relation of vessel diameter and fiber length to annual increment and age in 

 trunk of Acer pseudoplatanus. ( From Desch. ) 



2. This final tracheid size increases from the base of the trunk upward 

 to a maximum at a specific height and then decreases somewhat. 



3. The final size of tracheids in a branch is less than in the trunk but 

 depends to some extent on the position of the branch. 



Sanio's "laws" have been confirmed by most workers since his time 

 (Kribs, 1928, and others). Bailey and Shepard (1915), however, found 

 that, although the length of tracheids increases from the pith outward in 



