Notes on Bark Structure 



teristic of Taxodium, Cupressus, Thuja, Libocedrus, and 

 Juniperus. 



Calcium oxalate occurs in Pinus in the same form as in the 

 middle bark. In Taxodium, Cupressus, Thuja, Libocedrus, 

 and Juniperus, the radial membranes of all elements and in 

 Taxus the whole wall of the bast fibers and stone cells receive 

 deposits of very small crystals. 



All conifers have pith rays of a single row of cells, ex- 

 cepting in Pinus and Picea, where they broaden out to make 

 room for a resin canal. 



Key to the Genera: 



A. Bast fibers (on cross-section rounded-rectangular) in con- 

 centric mostly single rows; 3 rows of soft bast. 



1. Bast fibers very thick walled; here and there large 



stone cells with relatively thin walls. 



Sequoia 



2. Thick walled and thin walled fibers alternating; no 



stone cells. 



(a) Crystals in the walls of the bast fibers; bast 

 parenchyma thick walled, large pitted, free from 

 resin; scaly bark. 



Taxus 



(b) Crystals in all the radial walls; resin cysts; ring 

 "borke." (No safe distinctions in the structure 

 of the bast.) 



Taxodium 



Cupressus 



Thuja 



Libocedrus 



Juniperus 



B. Bast fibers wanting. 



1. No sclerenchyma except the hard walled cork layers; 



crystals prism-shaped. 



Pinus 



2. Scattered stone cells in the soft bast; isodiametric 



crystals. 



(a) Branched stone cells mostly combined in groups, 

 (x) Cork layer thin walled. 



, Abies 



(y) Cork hard walled ; often sclerotic phelloderm. 



Picea 



