354 



AMERICAN FORESTRY 



* J. _L 



dered ; such borders are always within 



Resin canals in white fir occur in of cells are similar. The pits are sim- 

 small .groups of two to six or more in pie, and only where resin cells touch 

 the early-wood, and usually near the tracheids do they appear to be bor- 

 inner boundary of concentric zones 

 (Figs. 5 and 6). These canals are al- 

 ways in direct communication with pith 

 rays (Figs. 5 A, 56, and 6), and are 

 surrounded by wood-parenchyma fibers 

 that contain starch during the winter 

 (Figs. 5 and 6 st. g.). Transverse sec- 

 tions of twigs cut from the top of the 

 tree show that young resin canals con- 

 sist of compact groups of cells, the cen- 

 tral portions of which are composed of 



the walls of the tracheids. The cells of 

 the young resin passages are filled dur- 

 ing the winter with starch (Figs. 7 and 

 9), which is eventually converted into 

 a fluid mass and later into resin. Trans- 



numerous round cells with wide cell 

 cavities, but in other respects are simi- 

 lar to the cells that are filled with starch 

 during the winter (Fig. 7). In the 

 early spring, when the vegetable pe- 

 riod begins, the starch is replaced by 

 a volatile oil, and during the first win- 

 ter there is no trace of resin in these 

 cells. Longitudinal sections show that 

 resin passages are surrounded by wood- 

 parenchyma fibers, the cells of which verse sections of two to four-year-old 

 are from two to three times as long as twigs exhibit structures similar^ to that 

 those in the center of the group. In of one-year-old twigs. There is, how- 

 other respects the inner and outer rows ever, a difference in cell content T ~ 



In 



