268 ANATOMY OF THE GYMNOSPERMS 



thin-walled, uniform in regular rows. Medullary rays not very numer- 

 ous, resinous, prominent, and distant 2-10 rows of tracheids. Resin 

 cells somewhat distant on the outer face of the summer wood, but 

 readily recognizable. 



Radial. Rays somewhat resinous throughout, the tracheids wholly marginal. 

 Ray cells chiefly straight except in the summer wood ; the upper and 

 lower walls medium, unequal, strongly pitted, especially in the summer 

 wood ; the terminal walls strongly pitted ; the lateral walls with very 

 small, oval, bordered pits with a lenticular orifice, which soon becomes 

 oblong and narrow, at first very variable and upwards of 5, soon uni- 

 formly 2, and in the summer wood i, per tracheid. Bordered pits 

 numerous, round or elliptical, in i row, sometimes in pairs. Pits on 

 the tangential walls of the summer wood rather numerous and flat, 

 not very large. Resin cells 20 //, wide, 150-275 /A long. 



Tangential. Rays medium, resinous, the cells unequal, chiefly broad but 

 variable, round or oval, more rarely oblong. 



3. T. caroliniana, Engel. 

 Hemlock 



Transverse. Growth rings medium, variable, the dense and prominent 

 summer wood composed of rather small and more or less rounded 

 tracheids, the transition from the spring wood rather abrupt, often 

 quite gradual, usually much less than, or again upwards of one half, 

 the spring wood. Spring tracheids rather large, uniform and thin- 

 walled in regular rows, usually elongated radially. Medullary rays 

 prominent, not very broad, i cell wide, distant 2-10 rows of tracheids. 

 Resin cells on the outer face of the summer wood prominent, resin- 

 ous, not very numerous, sometimes aggregated to form limited but 

 conspicuous and irregular layers on the inner face of the summer 

 wood. 



Radial. Rays uniformly somewhat resinous throughout, the tracheids 

 prominent, sometimes interspersed. Ray cells not conspicuously con- 

 tracted at the ends except in the summer wood, equal to 6-8 spring 

 tracheids, becoming much shorter in the summer wood ; the upper 

 and lower walls medium, very sparingly pitted except in the outer 

 summer wood ; the terminal walls coarsely pitted throughout ; the 

 lateral walls with small, narrowly bordered pits, the orifice at first 

 lenticular, at length narrowly oblong, at first 2-6, finally reduced to 

 i, per tracheid in the summer wood. Bordered pits round or elliptical, 

 very numerous, usually as broad as the tracheid, in I compact row. 

 Pits on the tangential walls of the summer tracheids numerous but 

 small and not very prominent. Resin cells on the outer face of the 

 summer wood 15 /JL wide, 185-310 p. long; those on the inner face 

 very short and cylindrical, irregular and unequal, and forming a con- 

 tinuous series without canals. 



Tangential. Rays rather numerous, medium, narrow, resinous, sometimes 

 constricted by the occasional and narrow, oblong tracheids ; the cells 

 somewhat unequal, chiefly oblong but rather variable, and sometimes 

 becoming oval. 



