PICEA 281 



the nutritive parenchyma thick-walled ; equal to 1-2 tracheids, devoid 

 of thyloses. Resin cells on the outer face of the summer wood few, 

 distant ; recognized by their thin walls and more advanced position, 

 and the sieve-plate structure of the terminal walls. 



Radial. Rays somewhat resinous throughout, with prominent, chiefly nar- 

 row, but often numerous, marginal tracheids, rarely interspersed. 

 Ray cells conspicuously straight throughout ; the upper and lower 

 walls rather thick, at first rather sparingly, but in the summer wood 

 very strongly, pitted ; the terminal walls coarsely pitted throughout ; 

 the lateral walls with rather small, oval, bordered pits, with a len- 

 ticular orifice, 2-6, abruptly reduced to i, per tracheid in the summer 

 wood. Bordered pits very large, with a large oval orifice, elliptical, 

 numerous, and often compact, two thirds the width of the tracheid, 

 in i row. Pits on the tangential walls of the summer wood few, 

 small, confined to the outermost tracheid wall. Resin cells 15 /A wide, 

 1 10-265 P- i n g> chiefly about 125^. 



Tangential. Rays rather numerous and resinous. The fusiform rays 

 narrow, the canal small without thyloses, the epithelium rather thick- 

 walled. Ordinary rays medium to high, contracted at the position of 

 the interspersed tracheids ; the parenchyma cells chiefly equal and 

 uniform, oblong, more rarely oval and broader. 



16. * PICEA, LINK. PLATES 50 AND 51 



Transverse. Growth rings variable, the transition to the usually prominent 

 summer wood gradual. Resin passages with or without thyloses, but 

 with thick-walled epithelium cells. Resin cells wholly wanting. 



Radial. Ray tracheids conspicuous, chiefly narrow, marginal, or some- 

 times interspersed. Terminal walls of the ray cells usually strongly 

 pitted. Tracheids wholly without spirals. 



Tangential. Fusiform rays chiefly narrow, with linear and often very 

 unequal and much-prolonged terminals ; the cells small and thick- 

 walled ; the central tract of I small resin passage without thyloses 

 but with thick-walled epithelium. Cells of the ordinary rays oblong, 

 more rarely oval. 



This genus is readily distinguished from Larix and Pseudotsuga by the 

 absence of resin cells and of spiral tracheids. 



SYNOPSIS OF SPECIES 



Ray cells (tangential) variable, round, oval, or oblong. 



Pits on the tangential walls of the summer wood chiefly or wholly 

 confined to the outermost wall. 



Pits on the lateral walls of the ray cells 1-3 per tracheid. 

 Ray cells (tangential) equal. 



Spring tracheids rounded-hexagonal, the structure not 

 very open. 



10. P. sitchensis. 



