II 



LA XGDOX—DIOOX SPIXL'LOSUM 



[1920 





P 





(5> 



(9 





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first pitted trachcids 5-6.5 mm., tracheids in the vicinity of the 

 cambium 7-9.8 mm. 



The protoxylem elements are of the reticulate and scalariform 

 types, and in passing from the metaxylem to the first formed 

 elements of the secondary wood all transitional stages occur in the 

 reduction of the scalariform structure into imperfectly formed, 

 multiseriate, bordered pits. 



While the majority of the tracheids of the secondary xylem 

 exhibit on their radial walls the multiseriate type of pitting 

 so characteristic of this 

 wood, many of the 

 tracheidal elements, 

 especially those consti- 

 tuting the secondarily 

 formed wood in the 

 upper trunk, have their 

 radial walls covered with 

 small bordered pits of a 

 very irregular arrange- 

 ment. 



In the wood of the 

 lower trunk tertiary 

 spiral thickenings of the 

 tracheid walls were ob- 

 served occurring in the 

 first few rings of growth 

 and also in the older 

 wood (fig. 1). These 

 spirals are not common 

 to all the tracheids, but 



are generally sporadic in their appearance and may be quite 

 inconspicuous. In some cases, however, they are characterized In- 

 considerable prominence, and are so compact as to suggest a reticu- 

 late rather than a spiral formation. 



In addition to the lignified elements of the wood there are 

 narrow elongated cells with transverse walls, the longitudinal stor- 

 age parenchyma. These cells, like those of the radially disposed 



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Fig. 1. — -Radial longitudinal section of tracheids 

 from lower portion of adult trunk: s, tertiary 

 spiral thickenings of tracheid walls; p, wood paren- 

 chyma; X225. 



