154 Forest Club Annual 



bast fiber bundles surrounded with a layer of parenchyma and 

 that in turn by layers -of sieve tubes and layers of parenchyma 

 alternating. In Gleditsia, only, a few aggregate crystals were 

 found. The parenchyma cells are always a little wider than 

 the bast fibers. The sieve tubes in Eobinia are short, just a 

 little wider than the parenchyma cells, and have simple cross 

 plates; those of Gleditsia are much shorter. The pith rays are 

 generally more than four row r s wide, and rarely contain stone 

 cells. 



Key to the Genera : 



Bast fiber bundles or plates in tangential rows cut through 

 by broad pith rays. 



1. Sieve tubes with lattice end-plates; bast fiber bundles 



enclosed by crystal cells, or at least accompanied by 

 them in large quantities. Bundle rows frequently 

 interrupted, accompanied by stone cells, between them 

 smaller bundles and single fibers. Bast fibers more 

 than 1 mm. long, crooked knotty. 



(a) Sieve tube elements many times broader than 

 parenchyma, with few sieve plates. 



Gymnocladus 



(b) Sieve tube elements not noticeably broad, with 

 large number of coarse pored sieve-plates; crys- 

 tal aggregates in the bast parenchyma and pith 

 rays. 



Gleditsia 



2. Sieve tubes with simple cross-plates ; bast fiber bun- 



dles surrounded by crystal cells, layers of bast fiber 

 bundles alternate with broader and larger celled lay- 

 ers of soft bast; no stone cells; pith rays of even 

 width. 



Robinia 



Acer. 



Outer bark. The superficial periderm develops in the 

 first vegetative period from the layer of cells immediately 

 under the epidermis. 



Middle bark. Collenchyma is present ; massive primary 

 strands are developed. Calcium oxalate is found in rhomboid- 

 al crystals. 



Inner bark. Stone cells slightly enlarged form an equal 



