32 D. P. PBNIIALLOW ON TWO SPECIES OF TERES, Etc. 



Medullary rays from two to twenty cells high, usually of one row, or occasionally of 

 three rows of cells at the centre. Resin tubes conspicuous in the autumn wood, but not 

 numerous. 



Transverse section Annual ring well defined, the autumn wood about equal to the spring 

 wood. Cells disposed in radial rows, usually about five rows between the medullary 

 rays. Eays somewhat abundant and narrow. The resin passages are not large — 

 55.7 - 103 8 // in diameter, — conspicuous and located wholly in the autumn wood, 

 chiefly forming a row on its inner face. Many annual rings wholly destitute of 

 resin passages. 



Radial section. The thick walled tracheids of the autumn wood provided with a single 

 row of bordered pits, somewhat irregularly disposed, the outer ring 6.9 - 13.8 // in 

 diameter. The thin w^alled tracheids of the spring wood with bordered pits in a 

 single row and often scattering, the outer ring 6.9 - 17.3 // in diameter. The 

 medullary rays somewhat abundant, the cells rather long and thin walled, and 

 showing pits. 



Tangential seclion. The medullary rays usually composed of a single series of cells, some- 

 times showing two or three rows at the centre; usually from two to twenty cells 

 high. No pits in the tangential walls. 



EXPLANATION OF PLATES. 



Plate II. 

 Piaa t'vanstoni. 



1.— Transverse section ehowiiig demarcation of growth ring, and a medullary ray. x 290. 

 —Tracheids showing bordered pits (a) of the spring wood, and (h) of the autumn wood, x 300. 

 —Medullary ray passing through the spring wood, showing structure and pits on radial walls, x 290. 



-Medullary ray passing through the autumn wood, showing pits on radial walls, x 300. 



■Tangential section of medullary rays of the ordinary form, x 290. 



■Tangential section of one of the broad medullary rays, x 266. 



Plate III. 

 Map showing lake ridges in vicinity of Chicago. 



