150 Forest Club Annual 



(x) Crystal cells with crystal aggregates in large 

 amounts accompanying the bast fibers. 



Corylus 



(y) Crystal aggregates only in soft bast; single 

 crystals accompanying the sclerotic elements 

 of the bast and the pith rays, 

 (m) Bast fiber plates in step-like layers. 



Ostrya 



( n ) Bast fibers grouped predominantly ra- 



Carpinus 



dially or scattered; primary scleren- 

 chyma ring is complete. 



(b) Bast fiber bundles, small amount and loosely ar- 

 ranged, not surrounded by crystal cells. 



Celtis 

 Fraxinus. 



Outer bark. The periderm develops during the first veg- 

 etative period. It originates in the layers of cells of the pri- 

 mary bark, immediately under the epidermis. The outer 

 bark remains thin as a consequence of the quick shedding of 

 the superficial layers. 



Middle bark. The primary bark is collenchyma like. 

 The stone cells appear only in isolated groups and at first in 

 the spaces between the primary bast bundles but without clos- 

 ing together to complete a sclerenchyma ring. Calcium ox- 

 alate occurs in the form of very delicate short crystal needles. 

 Inner bark. Bast fibers accompanied by stone cells from 

 regular tangential concentric bands. The bast fibers are of 

 typical form. The soft bast (always forms a very large part of 

 the inner bark. Calcium oxalate occurs as crystal sand or in 

 very minute pointed crystals. The pith rays are very often 

 only one or two rows wide. They contain a large amount of 

 crystals in the same form as the bast parenchyma. 



An important characteristic of Fraxinus bark is the par- 

 tial thickening of the pith ray cell walls where they pass be- 

 tween the sclerotic bundles. 

 Summary : 



Sclerenchyma groups are mixed with bast fibers and 

 stone cells in regular concentric arrangement; pith rays 

 occasionally partly sclerotic; bast fibers of typical form; 

 crystal sand and delicate prisms occur in the soft bast and 



