320 ANATOMY OF THE GYMNOSPERMS 



16. P. serotina, Michx. 



Pond Pine. Marsh Pine 



Trans-verse. Growth rings thick. Summer wood dense or in the narrow 

 rings rather open, often exceeding the spring wood, from which the 

 transition is commonly very abrupt ; the tracheids large and not very 

 uniform, hexagonal, in very regular rows. Spring tracheids large, 

 squarish, the walls thin. Resin passages numerous and large, chiefly 

 in the summer wood; the epithelium in i-several rows of very large, 

 round, and dark resinous cells, forming an extensive tract which is 

 often strongly eccentric to the canal. Medullary rays prominent, broad, 

 I cell wide, more or less resinous, distant 2-8 rows of tracheids. 



Radial. Rays more or less resinous throughout; the tracheids commonly 

 predominant, very variable in height, strongly reticulated throughout, 

 sparingly interspersed. Ray cells of one kind only, chiefly rather high, 

 more or less fusiform, equal to 4-6 spring tracheids, resinous ; the 

 terminal, upper, and lower walls thin and usually much broken out; 

 the lateral walls with very variable, lenticular pits, 1-4, rarely 5, per 

 tracheid, becoming very narrow and much prolonged slits in the sum- 

 mer wood. Bordered pits in i row or somewhat frequently in pairs, 

 and thus more or less 2-rowed, round, or elliptical. Pits on the tan- 

 gential walls of the summer wood wholly wanting. 



Tangential. Fusiform rays rather numerous, resinous, narrow, medium to 

 high, the terminals acute, more rarely prolonged, and composed of 

 small tracheids ; the inflated portion composed of large, thin-walled 

 cells usually much broken out. Ordinary rays medium, numerous, 

 broad, resinous, and presenting three principal aspects : (i) low rays of 

 i-several thin-walled, resinous parenchyma cells with small, termi- 

 nal tracheids ; (2) higher rays chiefly composed of very large, oblong, 

 and often strongly reticulated tracheids with i or 2 large, resinous 

 parenchyma cells much broken out ; and (3) the highest rays of several 

 oblong, resinous parenchyma cells with few terminal tracheids, or 

 again variously contracted through the presence of small, interspersed 

 tracheids. 



A tree 12-24 rn. high, with a trunk upwards of .90 m. in diameter. 

 Wood heavy, soft, not strong, brittle, coarse grained, and compact. 



Specific gravity 0.7942 



Percentage of ash residue 0.17 



Approximate relative fuel value 79.29 



Coefficient of elasticity in kilograms on millimeters . . 1170. 



Ultimate transverse strength in kilograms 497. 



Ultimate resistance to longitudinal crushing in kilograms 8079. 



Resistance to indentation to 1.27 mm. in kilograms . . 4740. 

 (Sargent) 



An uncommon species in low, peaty soil, ponds, and along the borders of 

 streams. North Carolina and south near the coast to the head of the 

 St. John's River, Florida (Sargent). 



