40 ROYAL SOCIETY OF CANADA 



tracheids medium to small, thickish walled, passing gradually into 

 the very thin summer wood. Summer wood of three to four tracheids 

 as in Thuya or Cupressus; the tracheids squarish, not very thick 

 walled, but strongly flattened in the outer row. Medullary rays 

 numerous, distant from 2 — 5 rows of tracheids. Resin canals wholly 

 wanting. Resin cells very numerous throughout the entire growth 

 ring, more or less in tangential rows, resinous contents not promin- 

 ent or massive, the color chiefly in the walls. 



Madial. — Grain much contorted. Resin cells numerous and prominent, about 

 15 to 1.75 mm. Bordered pits on the radial walls of the tracheids 

 medium to small, in one row, one-half the width of the tracheid, the 

 lenticular orifice diagonal, rather open. Medullary rays of resinous 

 color, but the resin not massive; cells all of one kind, chiefly straight; 

 the upper and lower walls thick and variable in width, strongly but 

 distantly pitted; the terminal walls thin, not pitted or locally 

 thickened, straight or often strongly curved; pits on the lateral walls 

 small, 1 — 2 per tracheid, when of the latter number in vertical series, 

 the oblong orifice at right angles to the cell axis. 



Tangential. — Rays very numerous and variable in height; strictly uniseriate; 

 the cells variable in size, chiefiy broadly oval or round, thick walled, 

 not conspicuously resinous. 



The characteristics thus set forth clearly establish the relations 

 of Podooarpus to the type of Cupressus or Thuya/ rather than to that 

 of Taxodium.- It may nevertheless be well to indicate the chief 

 characteristics in which the latter differs from the former. The sum- 

 mer wood of the growth ring is almost invariably double, constituting 

 a well defined character wihich, in addition to the usually great thick- 

 ness of the summer wood, serves to separate th© genus from all other 

 allied types. While in Podocarpus the rays are very numerous and 

 rarely separated by m^ore than five rows of tracheids, in Taxodium 

 they are distant from 2-11 rows. In radial section the resin cells 

 are only about 2 per 1.75 mm., thus making them at least seven times 

 less numerous (15 per 1.75 mm.) than in Podocarpus. The pits on 

 the lateral walls of the ray cells are upwards of seven in number, lying 

 in radial series, while in Podocarpus there is usually only one pit to 

 each tracheid, and when there are two, they lie in vertical series with 

 the oblong orifice also vertical. 



A careful consideration of these various details brings us to the 

 very obvious conclusion that the wood cannot be that of Podocarpus, 

 while it may be that of Glyptostrobus. But, as the only support for 

 the latter lies in associated lea,ves, while for Taxodium we have not 

 only the associated leaves but a stem structure which is, in all essential 

 respects that of the existing Tertiary distichum, we feel that there is 

 ample justification for referring the wood to the latter. 



^ Taxaceae «& Coniferae. Trans. R. See. Can., II., iv., 50. 

 ' lUd., 51. 



