292 ANATOMY OF THE GYMNOSPERMS 



of one or two kinds. Bordered pits on the tangential walls of the sum- 

 mer wood either numerous (Sec. I) or usually wanting (Sec. II). 

 Tracheids wholly without spirals. Resinous tracheids sometimes pres- 

 ent, the resin forming radial plates opposite the rays and simulating 

 Sanio's bands. 



Tangential. Fusiform rays chiefly large and broad ; the cells of the inflated 

 portion chiefly large and thin-walled ; the central tract occupied by 

 i large resin passage with thyloses and thin-walled epithelium. Ordi- 

 nary rays chiefly i -seriate, more or less conspicuously contracted by 

 the interspersed tracheids. 



SYNOPSIS OF SPECIES 



A. PINUS PROPER 



Existing Species 



Sec. I. Pits on the tangential -walls of the summer wood prom- 

 inent. Medullary tracheids prominent, sparingly interspersed, 

 their upper and lower walls not dentate. 



A. The lateral walls of the ray cells (radial) with small, numer- 

 ous, and more or less conspicuously bordered pits ; the upper 

 and lower walls thick and coarsely pitted ; the terminal walls 

 coarsely pitted ; the thick side walls (tangential) not inflated 

 or incurved. The rays sometimes show thin-walled cells with- 

 out pits, which are conterminous and interspersed. 

 Ray cells (radial) of I kind only, all thick-walled and strongly pitted. 



Rays nonresinous (radial), the tracheids numerous, marginal, often 

 interspersed. 



Pits on the lateral walls of the ray cells 1-4, chiefly 4, throughout, 

 but finally 2, per tracheid in the outer summer wood. 



Ray cells (tangential) conspicuously unequal and variable, 

 from round to oval or oblong, those of the low rays often 

 three times higher than wide. 



3. P. monophylla. 



Rays more or less resinous (radial), the tracheids marginal, sparingly 

 or rarely interspersed. 



Pits on the lateral walls of the ray cells 2-4 per tracheid throughout. 

 Ordinary rays (tangential) sparingly resinous, somewhat con- 

 tracted by occasionally interspersed, narrowly oval, or 

 oblong tracheids ; the cells equal and chiefly uniform, oval 

 to oblong, rarely narrow. 



i. P. Parryana. 



Ordinary rays (tangential) somewhat resinous, rather broad, 

 not perceptibly contracted by the occasionally interspersed 



