174 CONIFERALES [CH. 



field. In the characters of the normal wood this genus agrees 

 most closely with Cupressinoxylon and Mesembrioxylon. 



Cretaceous. 



VI. CEDROXYLON. 



In some species included in this genus contiguous and flattened 

 bordered pits are fairly common on the radial walls of the tracheids. 



Xylem-parenchyma, if present, confined to the late summer- 

 wood. 



Medullary rays uniseriate ; all the walls are pitted ; tracheids 

 may be present in the rays though they are usually absent. There 

 are 1 — 6 or rarely more pits in the field, either simple or apparently 

 bordered. Resin-canals confined to wounded regions. 



Jurassic (Triassic species doubtful) to Recent. 



VII. PITYOXYLON. (Including Piceoxylon and Pinuxylon.) 

 Though in the great majority of cases the tracheids of the 



secondary xylem have no spiral bands, the presence of such bands 

 in the recent genus Psevdotsuga shows that this feature may occur 

 in wood of the Pityoxylon type. 



Resin-canals present in the normal wood. Medullary rays of 

 two kinds, uniseriate rays consisting of parenchyma and, in many 

 cases, ray- tracheids, also fusiform rays with horizontal resin-canals. 

 The walls of the ray-tracheids are either smooth or irregularly 

 dentate. All the walls of the medullary-ray cells are pitted; 

 there may be one large simple pit in the field or several small, 

 apparently bordered, pits. 



Jurassic to Recent. 



VIII. PROTOPICEOXYLON. 



Similar to Pityoxylon except in the absence of horizontal 

 resin-canals in the normal wood; such horizontal canals as occur 

 are regarded as traumatic. 



Cretaceous to Tertiary. 



C. Genera in which Araucarian features, es'pecially as regards 

 the tracheal pitting, occur in association with characters met with in 

 recent Ahietineae. The genera included in this section ajford examples 

 of generalised types and do not resemble recent forms so closely as do 

 the other genera. 



