Notes on Bark Structure 145 



teristie of Ta.rodinnt, Cupi ' xxt/.s 1 , Thuja, Libocedrus, and 

 Jiinipf n/x. 



( 'alcium oxalate occurs in Pinus in the same form as in the 

 in i< Idle hark. In Taxodium, Cupressus, Thuja, Libocedrus, 

 and JuniperuSj the radial membranes of all elements and in 

 Ta.'-us the whole wall of the hast 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 



