Notes on Bark Structure 



(b) Numerous sieve plates arranged ladder-like. 

 (x) Pith rays in one row 



Alnus 

 (y) Pith rays in several rows. 



Betula 



B. Bast fibers present, but there are none, or only very few 

 stone cells. 



1. Extensive, closely packed bast fiber bundles in tan- 



gential rows accompanied by crystal cells; sieve 

 tubes with ladder-form plate system; pith rays of one 

 row. 

 (One species of Populus develops sclerenchyma.) 



Salix 

 Populus 



2. Small bast fiber bundles, loosely grouped and inde- 



pendent of crystal cells ; sieve tubes with simple cross- 

 plates; pith rays with more than one row. 



(a) Mucilage cells in soft bast; no stone cells. 



Ulmus 



(b) Latex tubes in the soft bast; sclerenchyma 

 present. 



Morus 



C. Bast fibers and sclerenchyma both always present. 



1. Bast fiber bundles grouped exclusively in large con- 



centric tangential rows, and accompanied by crystal 

 cells. 



(a) Sclerenchyma predominating; pith rays broad, 

 may become sclerotic, any place. 



Quercus 



(b) Regularity of the layers not influenced by the 

 small amount of sclerenchyma present; pith rays 

 one row. 



Castanca 



2. Bast fibers short and knotty combined with stone 



cells into plates and accompanied by crystal cells; 

 pith rays of several rows. 



Liquidambar 



3. The rows of bast fiber bundles frequently indistinct. 



(a) The bast fiber bundles (accompanied by crystal 

 cells. 



